"presentations" "Title(English)","Title(Japanese)","Presenter(s)(English)","Presenter(s)(Japanese)","Conference name(English)","Conference name(Japanese)","Presentation date","Invited talk","Language","Presentation type","Organizer(English)","Organizer(Japanese)","Venue(English)","Venue(Japanese)","URL","Description(English)","Description(Japanese)" "Epitaxial (111) Barrier Magnetic Tunnel Junctions with Fcc-CoFe Electrodes","Epitaxial (111) Barrier Magnetic Tunnel Junctions with Fcc-CoFe Electrodes","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","MRM2023/IUMRS-ICA2023 Grand Meeting","MRM2023/IUMRS-ICA2023 Grand Meeting","2023-12-11","","eng","oral_presentation","","","","","","Magnetoresistive random-access memory (MRAM) is one of the most important practical applications in spintronics due to its advantages such as non-volatility and high write endurance. MRAM data is stored in magnetic tunnel junctions (MTJs), which consist of an insulating layer (barrier) sandwiched between two ferromagnetic (FM) layers. Switching the relative alignment of the FM magnetizations from parallel to antiparallel results in an increase in resistance. This change is characterized by the tunnel magnetoresistance (TMR) ratio. A large TMR ratio is essential for high-performance MRAMs; thus, most MTJs employ bcc(001) type structures with large bulk spin polarization to enhance the TMR ratio utilizing the delta1 coherent tunneling effect. Recent (001) MTJs show a TMR ratio of 417% in Fe/MgO/Fe(001) and 631% in CoFe/MgO/CoFe(001). However, this (001) system has limitations such as few choices for FM materials. Recently, theoretical calculations predict giant TMR ratios in a new type MTJ with “fcc(111) structure”, which show the interfacial resonance driven TMR enhancement; e.g., Co/MgO/Co(111) with over 2000%. The novel interfacial spin polarization enhancement is promising for future MRAMs. However, the fabrication of a (111) barrier is challenging for growing fully fcc(111) MTJs. In this work, a fully epitaxial fcc(111) MTJ was successfully achieved by developing a Co90Fe10/Mg-Al-O (MAO) barrier/Co90Fe10(111) structure.","" "Nano artificial alloys in bulk-immiscible Ru-Cu system for spin-current generation","Nano artificial alloys in bulk-immiscible Ru-Cu system for spin-current generation","ハ ツォン, ソン ジェユアン, 温 振超, 介川 裕章, 三浦 良雄, 大久保 忠勝, Yukio Nozaki, 三谷 誠司","ハ ツォン, ソン ジェユアン, 温 振超, 介川 裕章, 三浦 良雄, 大久保 忠勝, Yukio Nozaki, 三谷 誠司","MRM2023/IUMRS-ICA2023 Grand Meeting","MRM2023/IUMRS-ICA2023 Grand Meeting","2023-12-11","","eng","oral_presentation","","","","","","In recent years, charge-to-spin current conversion has attracted considerable attention in recent years since the spin current could exert a spin-orbit torque (SOT) to the adjacent ferromagnetic material (FM), which enables to manipulate and even reverse the magnetization of FM without Joule-heating, leading to a huge potential for low-power-consumption spintronic devices, such as SOT-MRAM. To date, efficient spin current generation has been reported in heavy 5d metals with a strong spin-orbit coupling (SOC), such as W, Pt, and Ta. Light metals have a rather weak SOC, and they are usually not considered as efficient spin source materials, except for the case of a surface-oxidized copper film. Using the alternate monoatomic layer deposition (AMLD) method, here we report the successful preparation of a Cu50Ru50 nano artificial alloy in the bulk-immiscible Ru-Cu system and a remarkable enhancement in the spin-current generation in the negligible SOI system of the Cu50Ru50 film. ","" "Giant oscillatory tunnel magnetoresistance: an unsolved spin dependent tunneling puzzle","Giant oscillatory tunnel magnetoresistance: an unsolved spin dependent tunneling puzzle","シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 三谷 誠司","シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 三谷 誠司","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","2023-10-30","","eng","oral_presentation","","","","","","Magnetic tunnel junctions (MTJs) consisting in principle of an insulator sandwiched between two magnetic layers. The relative alignment of the magnetic layers moments in a parallel (P) or antiparallel (AP) state results in a low or high resistance state, respectively; the tunnel magnetoresistance (TMR) ratio. With the experimental demonstrations of the coherent tunneling mechanism using a crystalline MgO barrier in 2004, MTJs found their way into various applications, i.e., sensors and magnetic random-access memory (MRAM). Interestingly, this report observed oscillation of the tunnel magnetoresistance (TMR) ratio as function of the barrier thickness with an oscillation period of 0.32 nm in Fe/MgO/Fe(001). Since then, oscillations with similar periods have been reported in other systems with different materials. However, compared to the total number of publications on TMR, MTJs with TMR oscillation are rarely observed. Additionally, theoretical calculations satisfactorily explaining the observed behavior are lacking making TMR oscillations a longstanding puzzle. In this presentation, we will highlight our experimental observations of the details of the giant TMR demonstration with additional information on the TMR oscillations.","" "Perpendicular Magnetic Tunnel Junctions with a Monoatomic-Layer-Controlled CoPt(111) layer and a MgO(111) Barrier ","Perpendicular Magnetic Tunnel Junctions with a Monoatomic-Layer-Controlled CoPt(111) layer and a MgO(111) Barrier ","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 大久保 忠勝, Kwangseok Kim, 介川 裕章, 三谷 誠司","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 大久保 忠勝, Kwangseok Kim, 介川 裕章, 三谷 誠司","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","2023-10-30","","eng","oral_presentation","","","","","","The development of magnetic tunnel junctions (MTJs) with large tunnel magnetoresistance (TMR) and strong perpendicular magnetic anisotropy (PMA) is essential for ultra-high density magnetoresistive random access memories (MRAMs). Nowadays, the bcc(001)-type MTJs, i.e., Fe/MgO/Fe and CoFeB/MgO/CoFeB, which exhibit enhanced TMR ratios due to the delta1 coherent tunneling effect and PMA at a MgO interface, are used as MRAM cells. However, the limited material choices within the (001)-type MTJs and the limited interfacial PMA energies restrain further progress in perpendicular MTJs (p-MTJs). Recently, theoretical calculations have predicted that the fcc(111)-type p-MTJs using a MgO(111) barrier and Co-based PMA alloys, such as L11-CoPt, exhibit large TMR ratios over 2000% due to an interfacial resonant tunneling effect. In this work, we report the first TMR observation by developing an epitaxial L11-CoPt(111)/MgO(111)/CoFeB p-MTJ using monoatomic monolayer control by sputtering. ","" "Inverse tunneling magnetoresistance driven by interfacial resonance states in a (001)-oriented FeRh/MgO/FeCo junction","Inverse tunneling magnetoresistance driven by interfacial resonance states in a (001)-oriented FeRh/MgO/FeCo junction","温 振超, シャイケ トーマス, ハ ツォン, 増田 啓介, 介川 裕章, 大久保 忠勝, 三谷 誠司","温 振超, シャイケ トーマス, ハ ツォン, 増田 啓介, 介川 裕章, 大久保 忠勝, 三谷 誠司","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","2023-10-30","","eng","oral_presentation","","","","","","The magnetic tunnel junction (MTJ) consists of two ferromagnetic layers separated by a thin insulating layer and the relative change in MTJ resistance is called tunneling magnetoresistance (TMR). The MTJs with large TMR are indispensable for spintronic applications, such as magnetic field sensors and magnetic random access memories. The TMR effect conventionally originates from the spin polarization of ferromagnetic layers and the coherent tunneling through the MgO(001) barrier. Recently, Masuda et al., reported interfacial resonance effect can contribute to a giant tunnel magnetoresistance in (111)-oriented MTJs. Engineering materials and interfaces of MTJs exhibiting large and unique TMR properties are of particular importance for broadening the applications of MTJs. In this study, we report an inverse TMR effect in an epitaxial MTJ with a core structure of FeRh/MgO/FeCo MTJs originating from the interfacial resonance effect. All the films were deposited on MgO(001) substrates by magnetron sputtering. Microstructure analyses indicate a fully epitaxial growth with (001) orientation in the MTJ stack. It was found that the TMR is inversed with changing the applied voltage from positive to negative. When the applied voltage is -0.6V, the value of TMR is about -20%; and when the voltage becomes 0.6V, the value of TMR becomes about 20%. The positive voltage indicates that the current flows from FeCo to FeRh. We further performed first-principles calculations to figure out the mechanism of the TMR property. The electronic band structures show that minority electrons with Δ2 and Δ5 symmetries are half-metallic at the Fermi level of the FeRh electrode. It is confirmed that the TMR characteristics arise from the interfacial resonance states, which can be found from the k// dependence of transmittance and the energy dependence of spin-resolved local density of states of interfacial atoms of FeRh and FeCo electrodes. ","" "Epitaxial Ru-Mo(0001) Thin Films with Nano-Scale Resistivity Gradient for Charge-Spin Conversion","Epitaxial Ru-Mo(0001) Thin Films with Nano-Scale Resistivity Gradient for Charge-Spin Conversion","タン カ, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 能崎 幸雄, 三谷 誠司","タン カ, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 能崎 幸雄, 三谷 誠司","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","2023-10-30","","eng","oral_presentation","","","","","","In this study, the Ru-Mo systems are investigated to explore this intriguing phenomenon. Since Ru and Mo are materials reported to have small spin Hall interactions, the Ru-Mo systems may give us a suitable platform to demonstrate the SVC-generated spin currents. The Ru1-xMox thin films with x from 0 to 50% were epitaxially grown on c-plane sapphire substrates by magnetron co-sputtering using individual Ru and Mo targets. Structural analyses show the RuMo films have a hcp structure with an epitaxial relationship of RuMo(0001)[11-20] // Al2O3(0001)[10-10]. In accordance with the Nordheim’s rule, the resistivity of the films gradually increases from 7 to 53 μΩcm with increasing Mo composition from 0 to 50%, which indicates that the gradient electrical resistivity can be achieved by controlling the compositions in the RuMo films. We further designed and fabricated a Ru1-xMox (7.7 nm)/CoFeB(0-10 nm) structure, as illustrated in Fig. 1(a), where the Ru1-xMox layer has a gradient composition starting from x = 50% (bottom) to 0% (top). The measurements of the spin-torque ferromagnetic resonance (ST-FMR) were performed to characterize the spin-transport properties. As shown in Fig. 1(b), a clear voltage signal consisting of antisymmetric and symmetric line shapes was observed. The damping-like torque efficiency ξDL of the gradient Ru1-xMox film was evaluated to be ~1.6% by investigating the CoFeB thickness dependence of torque efficiency. In addition, the ξDL of a reference sample with a Ru50Mo50/CoFeB structure was estimated to be ~0.4%. The results indicate that the SVC could be mainly responsible for the spin current generation in the gradient Ru1-xMox films. ","" "Three Types of Nano Crystal Domain Structures in Fully Epitaxial fcc-Co/MgO/Co(111) Magnetic Tunnel Junctions","Three Types of Nano Crystal Domain Structures in Fully Epitaxial fcc-Co/MgO/Co(111) Magnetic Tunnel Junctions","ハ ツォン, 増田 啓介, ソン ジェユアン, シャイケ トーマス, 温 振超, 介川 裕章, 三浦 良雄, 大久保 忠勝, 宝野 和博, 三谷 誠司","ハ ツォン, 増田 啓介, ソン ジェユアン, シャイケ トーマス, 温 振超, 介川 裕章, 三浦 良雄, 大久保 忠勝, 宝野 和博, 三谷 誠司","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","2023-10-30","","eng","oral_presentation","","","","","","The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs) has been extensively investigated for practical spintronic devices such as non-volatile magnetoresistive random access memories (MRAMs). To date, large TMR ratios exceeding 100% have been reported in bcc-(001) MTJs, e.g. Fe/MgO/Fe and CoFeB/MgO/CoFeB, which have been explained by the coherent tunneling through ""bulk” Δ1 states. In a recent theoretical calculations, a large TMR ratio over 2000% was predicted in the fcc-Co(111)/MgO(111)/Co(111) MTJ because of a different tunneling mechanism, i.e., “interfacial” resonant effect of d-p antibonding states. More recently, a first TMR ratio (35%) was demonstrated by Song et al. in a fully epitaxial fcc(111) MTJ with a structure of (Co90Fe10) CoFe/MgO/CoFe. In this study, detailed microstructure and its relationship to the TMR properties in the CoFe/MgO/CoFe(111) MTJ were systematically investigated using a combination of atomic-resolution scanning transmission electron microscope (STEM) observations and first-principles calculations. ","" "Record for tunnel magnetoresistance of 631% at room temperature with barrier interface control technology","Record for tunnel magnetoresistance of 631% at room temperature with barrier interface control technology","介川 裕章","介川 裕章","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","The 68th Annual Conference on Magnetism and Magnetic Materials (MMM2023)","2023-10-30","","eng","oral_presentation","","","","","","Tunnel magnetoresistance (TMR) observed in magnetic tunnel junctions (MTJs) has a history of almost half a century since the first report by Julliere in 1975, and is the basis for many of today’s spintronic applications. Significant progress in the room temperature (RT) TMR ratios has been achieved with two breakthroughs that have determined the practical applications: the first was the observation of RT TMR ratios above ten percent in 1995, and the second was the observation of the giant TMR effect due to the coherent tunneling mechanism in 2004. These observations have greatly contributed to the development of high-capacity recording using TMR heads in hard disk drives. Here, we demonstrated a TMR ratio of up to 631% at RT (1134% at 10 K) by introducing a Co50Fe50 (CoFe)/MgO/CoFe structure. The significant improvement in the TMR ratio are crucial steps for the development of future spintronic applications. Along with the increase in TMR ratio, the unsolved effect, namely TMR oscillation, is more pronounced in the high-quality epitaxial MTJs. The TMR ratio oscillates significantly as a function of barrier thickness with a period of ~0.3 nm, and the peak-to-valley differences at RT reach 141% in the CoFe/MgO/CoFe. The large oscillation cannot be explained by standard coherent tunneling theories. Therefore, further clarification of the oscillatory behavior may provide an important clue to truly large TMR ratios, e.g., >1000% at RT.","" "Theoretical study for (111)-oriented magnetic tunnel junctions with SrTiO3 barriers","SrTiO3を用いた(111)配向磁気トンネル接合の理論研究","増田 啓介, 伊藤博介, 園部義明, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 伊藤博介, 園部義明, 介川 裕章, 三谷 誠司, 三浦 良雄","第47回 日本磁気学会学術講演会","第47回 日本磁気学会学術講演会","2023-09-27","","jpn","oral_presentation","","","","","","","磁気ランダムアクセスメモリ (MRAM) への応用のため, 磁気トンネル接合 (MTJ) は高いトンネル磁気抵抗比 (TMR比) と大きな垂直磁気異方性 (PMA) を有する必要がある. このような主眼から, 我々はこれまでfcc強磁性体の[111]方向を積層方向とした新規(111)配向MTJについて理論研究を行ってきた. 我々はトンネル障壁としてMgOを用いたMTJについて解析を行い, 2000%を超える高いTMR比とL11強磁性合金の電子構造に由来する大きな垂直磁気異方性が両立することを実証してきた. しかし(111)配向MTJのトンネル障壁はMgOに限られたものではなく, その他の物質について検討することは新規MTJの更なる可能性を開拓する上で重要である. そこで本研究では, トンネル障壁として歴史的に重要な役割を果たしてきたSrTiO3を取り上げ, これを用いた(111)配向MTJのTMR効果について理論検討を行う." "Fabrication of epitaxial MgAl2O4/L10-FePt(001) stacks for perpendicular magnetic tunnel junctions","垂直型強磁性トンネル接合のためのエピタキシャルMgAl2O4/L10-FePt(001)構造の作製","金澤 朋希, シャイケ トーマス, 埋橋 淳, 大久保 忠勝, 介川 裕章, 三谷 誠司, 柳原 英人","金澤 朋希, シャイケ トーマス, 埋橋 淳, 大久保 忠勝, 介川 裕章, 三谷 誠司, 柳原 英人","第47回日本磁気学会学術講演会","第47回日本磁気学会学術講演会","2023-09-27","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)はハードディスクの磁気ヘッドや、不揮発性磁気メモリ(MRAM)の記憶素子として利用されている。今後、MRAMの高密度化による半導体メモリの一部置き換えを実現するためには、nmスケールへMTJ微細化が必要である。現在MRAM用の垂直磁化MTJ(p-MTJ)では、CoFeB/MgO界面に誘起される垂直磁気異方性(PMA)が利用されているが、MTJ微細化により十分な熱安定性を確保することが困難になっている。この問題の解決のため、極めて高い磁気異方性(~70 Merg/cm3)を示すL10型FePt(001)がp-MTJの磁性層として有望である。しかし、FePtとMgOバリアとの10%近い大きな格子不整合があることから高品位なMTJの作製が困難である。本研究では、高品位FePt系MTJの実現のため、MgOよりも格子整合性がよいスピネル(MgAl2O4系材料)をバリアとして用い、その上にFeとPtの交互原子積層により垂直磁化を持つFePt(001)エピタキシャル層を400度以下のプロセスで実現した。" "CoFe/MgO/CoFe(001) magnetic tunnel junctions with giant tunnel magnetoresistance exceeding 630% at room temperature","CoFe/MgO/CoFe(001) magnetic tunnel junctions with giant tunnel magnetoresistance exceeding 630% at room temperature","シャイケ トーマス, 温 振超, 介川 裕章, 三谷 誠司","シャイケ トーマス, 温 振超, 介川 裕章, 三谷 誠司","第47回日本磁気学会学術講演会","第47回日本磁気学会学術講演会","2023-09-27","","eng","oral_presentation","","","","","","Magnetic tunnel junctions (MTJs) are a key component for spintronics applications, such as sensors and magnetic random-access memory (MRAM). However, the resistive change of MTJs, i.e., TMR ratio, is low even after several decades of research and development as compared to other nonvolatile competing solutions, such as resistive RAM. Recently, we have demonstrated increased room temperature (RT) tunnel magnetoresistance (TMR) ratio exceeding 400% using single-crystal Fe/MgO/Fe and Fe/MgAlO/Fe MTJs, doubling the previously reported ratios of Fe-based MTJs by careful optimization of several key layers. The results further emphasized the important role of interface properties, i.e., roughness and oxidation, on the transport properties. In this work, we show the effect of tuning of Mg and CoFe insertion layers at the interfaces on the transport properties leading to increased RT TMR ratios.","" "Observation of a tunnel magnetoresistance ratio exceeding 630% at room temperature","630%を超える室温トンネル磁気抵抗比の観測","シャイケ トーマス, 温 振超, 介川 裕章, 三谷 誠司","シャイケ トーマス, 温 振超, 介川 裕章, 三谷 誠司","2023年第84回応用物理学会秋季学術講演会","2023年第84回応用物理学会秋季学術講演会","2023-09-19","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)はハードディスクのリードヘッドや磁気メモリ(MRAM)に用いられており、スピントロニクス応用を担う中核的素子である。今後、より高感度な磁気センサーや高密度なMRAMを実現するためには、室温のトンネル磁気抵抗比(TMR比)を現在よりも格段に大きくすることが求められている。しかし、2008年のIkedaらによる604%の報告を最後にTMR更新は報告されていない。この停滞を打破するため我々はFe/MgO/Feの基本MTJ積層に立ち返り、最新のエピタキシャル成長技術を用いてMgO界面の再開発を行った。その結果、従来の約2倍となる400%以上の室温TMR比が実現された。低温ではFe/MgO/Feの理論計算での典型的な値に匹敵する1000%に達しており、高品位結晶の実現と界面構造の改善がTMR比増大のカギを握っていることを明らかにした。本研究ではCoFe/MgO/CoFe構造を採用しMgO界面の追加最適化を行うことで室温TMR比の最高値を更新する631%を達成した。" "High-quality epitaxial growth of altermagnetic RuO2 films using reactive sputtering","High-quality epitaxial growth of altermagnetic RuO2 films using reactive sputtering","ハ ツォン, 温 振超, 介川 裕章, 三谷 誠司","ハ ツォン, 温 振超, 介川 裕章, 三谷 誠司","第84回応用物理学会秋季学術講演会","第84回応用物理学会秋季学術講演会","2023-09-19","","eng","oral_presentation","","","","","","We investigate the microstructure of epitaxial growth of RuO2 films on substrates of MgO(001), Al2O3(0001) and Al2O3(11̅02). RuO2 films were grown by rf reactive magnetron sputtering using a pure Ru target and Ar + O2 gas mixture at 300 °C. Post-annealing in a high vacuum was performed to improve the crystallinity and resistivity. The film quality was evaluated using atomic force microscopy (AFM), x-ray diffraction (XRD) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). We found that single-crystalline epitaxial growth of RuO2 film was successfully achieved on Al2O3(11̅02) substrates (Figs. 1a and 1b), whilst two and three kinds of domain structures were obtained on MgO(001) and Al2O3(0001), respectively, as verified by the Ф-scan XRD analysis. AFM images show very flat surfaces of the films grown on Al2O3(11̅ 02), with an average roughness of ~0.26 nm. The optimal annealing temperature was determined to be 600 °C, which reduced the resistivity of films to a value of 51.5 μΩ·cm, much lower than those in previous studies. HAADF-STEM images in Figs. 1c and 1d further reveal that the RuO2 film was highly crystalline and had an epitaxial relationship of RuO2(101)[010] // Al2O3(11̅02)[112̅0]. The Néel temperature was also determined to be around 390 K from the temperature dependence of resistivity measurement.","" "Development of spinel barriers for high performance magnetic tunnel junctions","Development of spinel barriers for high performance magnetic tunnel junctions","介川 裕章","介川 裕章","The 6th International Conference of Asian Union of Magnetics Societies (IcAUMS2023)","The 6th International Conference of Asian Union of Magnetics Societies (IcAUMS2023)","2023-08-14","","eng","oral_presentation","","","","","","Tunnel magnetoresistance (TMR) devices, also known as magnetic tunnel junctions (MTJs), play a central role used in spintronic applications, such as hard disk drives and non-volatile magnetoresistive random access memories (MRAMs). The discovery of a new tunnel barrier materials for MTJs has boosted significant progress in MTJs [1]. In the early stages of the development, amorphous alumina was used for a MTJ barrier. After theoretical predictions of the giant TMR effect due to the spin-dependent coherent tunneling, a crystalline magnesium oxide (MgO) became the standard barrier for MTJs. Nowadays, CoFeB/MgO/CoFeB structured MTJs are used in most applications due to their excellent compatibility with semiconductor technology in addition to large TMR ratios at room temperature (RT). However, there is a limited choice of MTJ materials, which significantly limits the MTJ application areas. In particular, the large lattice mismatch between MgO and standard magnetic layers prevents the innovation of the MTJ structure. Therefore, this situation has made it difficult to further improve their performance. In the present talk, I will talk about our development of high performance MTJs using non-magnetic spinel oxide materials. ","" "Room temperature tunnel magnetoresistance new record of 631%, toward new spintronic devices","Room temperature tunnel magnetoresistance new record of 631%, toward new spintronic devices","介川 裕章","介川 裕章","The 34th Magnetic Recording Conference (TMRC 2023)","The 34th Magnetic Recording Conference (TMRC 2023)","2023-07-31","","eng","oral_presentation","","","","","","We demonstrated a tunnel magnetoresistance (TMR) ratio of up to 631% and giant TMR oscillation effect at room temperature using CoFe/MgO/CoFe(001) based epitaxial magnetic tunnel junctions. The maximum TMR ratio at low temperature reached 1134%, corresponding to the tunneling spin polarization of 0.923. The improvement of the MTJ nanostructure by fine-tuning of the barrier interface states for the upper and lower MgO sides is responsible for this significant enhancement of the maximum TMR ratio. The demonstration of giant TMR ratios at room temperature using MTJ interface control will pave the way for improving the sensitivity of TMR heads and increasing the capacity of a magnetoresistive memory. Surprisingly, the TMR ratio clearly oscillates with the MgO thickness in the CoFe/MgO/CoFe, the amplitude of which was much larger than in the Fe/MgO/Fe(001) reports. ","" "Improved dielectric breakdown of magnetic tunnel junctions using a lattice-matched MgAl2O4 barrier","Improved dielectric breakdown of magnetic tunnel junctions using a lattice-matched MgAl2O4 barrier","介川 裕章, 温 振超, 葛西 伸哉, 埋橋 淳, 大久保 忠勝, 宝野 和博, 三谷 誠司, Shinto Ichikawa, Katsuyuki Nakada","介川 裕章, 温 振超, 葛西 伸哉, 埋橋 淳, 大久保 忠勝, 宝野 和博, 三谷 誠司, Shinto Ichikawa, Katsuyuki Nakada","MML2023 (11th International Symposium on Metallic Multilayers)","MML2023 (11th International Symposium on Metallic Multilayers)","2023-07-24","","eng","oral_presentation","","","","","","For spintronic devices based on magnetic tunnel junctions (MTJs), such as a magnetoresistive random access memory (MRAM) and a hard disk drive read-head, improving the dielectric breakdown voltage of MTJs is one of the most important issues in their applications. In recent devices, the thickness of MgO, which is the typical MTJ barrier layer, has become extremely thin, less than 1 nm, making it difficult to maintain good device reliability for a long period of time due to the significant drop in the breakdown voltage. Spinel MgAl2O4 (MAO) based barrier is known as a promising alternative to MgO as an MTJ barrier material. Recently, a giant tunnel magnetoresistance (TMR) ratio exceeding 420% at room temperature has been achieved in the Fe/MAO/Fe structure; thus, the MAO is expected to be a barrier that can realize excellent TMR properties. Due to the good lattice matching of MAO with bcc ferromagnetic layers (mismatch < 1%), the MAO barrier is advantageous to reduce the lattice imperfections near the barrier interfaces, where breakdowns are likely to occur at low bias voltages. Indeed, good time-to-dielectric-breakdown characteristics have been reported in Fe/MAO/Fe MTJs. However, the relationship between improved barrier interface structure and improved breakdown voltage has not yet been investigated. In this study, we investigated the breakdown characteristics and barrier interface nanostructure in epitaxial CoFe/MAO/CoFe(001) MTJs.","" "Analysis of large oscillations in tunnel magnetoresistance and resistance of Fe/Mg4Al-Ox/Fe magnetic tunnel junctions","Analysis of large oscillations in tunnel magnetoresistance and resistance of Fe/Mg4Al-Ox/Fe magnetic tunnel junctions","シャイケ トーマス, 温 振超, 葛西 伸哉, 介川 裕章, 三谷 誠司","シャイケ トーマス, 温 振超, 葛西 伸哉, 介川 裕章, 三谷 誠司","MML2023 (11th International Symposium on Metallic Multilayers)","MML2023 (11th International Symposium on Metallic Multilayers)","2023-07-24","","eng","oral_presentation","","","","","","Magnetic tunnel junctions (MTJs) are used as the basic building blocks for various spintronics applications. They have been extensively studied both experimentally and theoretically to increase the tunnel magnetoresistance (TMR). This has led to the theoretical prediction and experimental exploitation of the so-called delta1 coherent tunneling mechanism which is necessary for giant TMR in (001)-oriented MTJs. Notably, oscillation effect associated with the giant TMR effect is often observed when using a high-quality epitaxial MTJ structure, which is absent in most theoretical calculations: TMR oscillation with a barrier thickness even at room temperature (RT) with a period of ~0.3 nm. We have recently reported on large TMR oscillations in highly (001) oriented epitaxial Fe/Mg4Al-Ox/Fe with peak TMR ratios exceeding 420%. Here, we investigated the TMR and resistance area (RA) oscillation behavior in details using the Fe/Mg4Al-Ox/Fe MTJs. We measured an array of over 450 MTJs on the same wafer and report a significant change of the oscillation behavior at RT, deviating from the commonly observed sine function.","" "Advancing TMR through Epitaxial Technology: Reaching 631% at Room Temperature","Advancing TMR through Epitaxial Technology: Reaching 631% at Room Temperature","介川 裕章","介川 裕章","The 2023 Spintronics Workshop on LSI ","The 2023 Spintronics Workshop on LSI ","2023-06-12","","eng","oral_presentation","","","","","","集積回路に関する国際会議The 2023 VLSI Symposium on VLSI Technology and Circuitsのサテライト国際ワークショップとして開催されたThe 2023 Spintronics Workshop on LSIにおいて、最新のトンネル磁気抵抗素子の特性向上について講演を行う。CoFe/MgO/CoFe構造の素子の開発を行うことによって、世界最大の室温磁気抵抗比631%が得られたこと、今後の進展について報告を行う。","" "Spin current generation in highly conductive Ru/Cu epitaxial heterostructures","Spin current generation in highly conductive Ru/Cu epitaxial heterostructures","温 振超, ソン ジェユアン, ハ ツォン, シャイケ トーマス, 介川 裕章, 大久保 忠勝, 能崎 幸雄, 三谷 誠司","温 振超, ソン ジェユアン, ハ ツォン, シャイケ トーマス, 介川 裕章, 大久保 忠勝, 能崎 幸雄, 三谷 誠司","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","Significant spin current generation from highly conductive materials is promising for spintronic applications, such as spin-orbit-torque magnetic random-access memories. In this work, we fabricated epitaxial Ru/Cu heterostructures with interface engineering where 1-nm-thick Ru and Cu layers were alternately deposited at the interface. The spin current generation in the heterostructures was evaluated by unidirectional spin Hall magnetoresistance and spin-torque ferromagnetic resonance. A sizable spin Hall efficiency (~-2%) was achieved in the Ru/Cu sample with a sharp interface which may result from the interface spin filtering effect. Increased spin Hall efficiency (~-4%) was observed in the interface-engineered samples which could be attributed to the intrinsic contribution from lattice distortion and local band structure near the interface. The effective spin Hall conductivity was estimated to be comparable to that of Platinum.","" "Nano artificial alloys in bulk-immiscible Ru-Cu system for spin-current generation","Nano artificial alloys in bulk-immiscible Ru-Cu system for spin-current generation","ハ ツォン, ソン ジェユアン, 温 振超, 介川 裕章, 三浦 良雄, 大久保 忠勝, 能崎 幸雄, 三谷 誠司","ハ ツォン, ソン ジェユアン, 温 振超, 介川 裕章, 三浦 良雄, 大久保 忠勝, 能崎 幸雄, 三谷 誠司","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","Spin current is a flow of spin angular momentum and is considered as an ideal information carrier for spintronic devices due to the merit of low power consumption. However, an efficient conversion between charge and spin current usually depends on the strong spin-orbit interaction (SOI) in heavy 5d metals such as Pt and Ta. Here we report a remarkable enhancement in the spin transport property in a negligible SOI system of Cu50Ru50. Although Cu-Ru system is bulk-immiscible, the Cu50Ru50 film, prepared by the alternate monoatomic layer deposition method, is a nano artificial alloy and the atomic-scale intermixing has been directly confirmed by atomic-resolution energy-dispersive X-ray spectroscopy. Compared with pure Cu and Ru metals, we find 100 times enhancement in unidirectional spin Hall magnetoresistance detected in this nano artificial alloy, which is comparable to values in Pt and Ta. Our findings are expected to be applicable to other bulk-immiscible metallic systems with a weak SOI, which paves a way for designing novel alloy films with desirable properties and functionalities.","" "Effects of Elemental Doping and Interface Engineering on Spin-Orbit Torques in CoSi-based Topological Semimetal Thin Films","Effects of Elemental Doping and Interface Engineering on Spin-Orbit Torques in CoSi-based Topological Semimetal Thin Films","タン カ, 温 振超, 関 剛斎, 介川 裕章, 三谷 誠司","タン カ, 温 振超, 関 剛斎, 介川 裕章, 三谷 誠司","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","This study reports on how Ni or Fe doping and interface engineering affect the spin-orbit torques (SOTs) generated from the topological semimetal CoSi. The CoSi films deposited on c-plane sapphire substrates are crystalized in a B20 structure and textured in (210) orientation even after 15% Ni or 26% Fe doping. We characterized the SOTs from the films exerted onto the magnetization of a CoFeB layer by harmonic Hall and spin-torque ferromagnetic resonance measurements. The results show that the spin Hall efficiency ξSH of the CoSi decreases after Ni or Fe doping. According to the electrical conductivity dependence of the spin Hall conductivity, which locates at the regime of intrinsic mechanism of spin Hall effect, the reduction of ξSH may result from the degraded topological electronic structures of CoSi by doping. It is also found that inserting a Cu layer at the Co(Ni, Fe)Si/CoFeB interface enhances the ξSH. The enhancement can be due to the improved interfacial spin transparency between the Co(Ni, Fe)Si and CoFeB layers.","" "Sawtooth-like giant oscillation of tunnel magnetoresistance in epitaxial Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","Sawtooth-like giant oscillation of tunnel magnetoresistance in epitaxial Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","シャイケ トーマス, 温 振超, 葛西 伸哉, 介川 裕章, 三谷 誠司","シャイケ トーマス, 温 振超, 葛西 伸哉, 介川 裕章, 三谷 誠司","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","A 0.3-nm-period tunnel magnetoresistance (TMR) oscillation with a barrier thickness observed in high-quality magnetic tunnel junctions (MTJs) is a longstanding and unsolved phenomenon in spintronics since it observed in an epitaxial Fe/MgO/Fe(001) MTJ in 2004. Here, we report on an enhanced TMR oscillation effect exceed 125% peak-to-valley difference at room temperature in epitaxial MTJs by introducing a spinel-based Mg4Al-Ox barrier: Fe/Mg4Al-Ox/Fe(001). We observe saw-tooth wave shaped oscillations in a TMR ratio with the Mg4Al-Ox thickness. Interestingly, this uncommon shape was derived from a staircase-like increase in ln(RA) vs. Mg4Al-Ox thickness, where RA is the resistance area product. After removing the exponential background of resistances, spike-like oscillation components were clearly observed. Our findings will provide helpful information toward understanding the physical origin of the oscillation effect in MTJs.","" "Co90Fe10/Mg-Al-O/Co90Fe10 magnetic tunnel junctions with a fully epitaxial fcc (111) structure","Co90Fe10/Mg-Al-O/Co90Fe10 magnetic tunnel junctions with a fully epitaxial fcc (111) structure","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","Co90Fe10 (CoFe)/Mg-Al-O (MAO)/Co90Fe10 magnetic tunnel junctions (MTJs) with a fully epitaxial fcc (111) structure were fabricated on an Ru buffered sapphire(0001) substrate. Highly quality epitaxial growth from the Ru buffer to the top CoFe layer was achieved through optimization of deposition processes e.g., substrate treatment, sputtering, electron beam evaporation, and in-situ post-annealing. Flat interface structure and good crystallinity were confirmed by scanning transmission electron microscopy of the cross-section of an MTJ. Interestingly, the observation reveals introduction of periodic misfit dislocations at the CoFe/MAO interfaces due to their large (~18%) lattice mismatch. Prepared MTJs showed tunnel magnetoresistance (TMR) ratio of up to 37% at room temperature and 47% at 10 K. ","" "Large tunnel magnetocapacitance effect in FeCo/MgAlO/FeCo(001) magnetic tunnel junctions","Large tunnel magnetocapacitance effect in FeCo/MgAlO/FeCo(001) magnetic tunnel junctions","Yuto Shibata, Kenta Sato, 介川 裕章, Hideo Kaiju","Yuto Shibata, Kenta Sato, 介川 裕章, Hideo Kaiju","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","We investigate the frequency characteristics and voltage dependence of tunnel magnetocapacitance (TMC) in FeCo/MgAlO/FeCo(001) epitaxial magnetic tunnel junctions (MTJs). We have successfully observed a large TMC ratio of up to 456% at 140 Hz and 75 mV, which is the largest value ever reported for MTJs. The frequency characteristics and voltage dependence of the observed TMC characteristics can be reasonably explained by the calculation based on the extended Debye-Frölich model. ","" "Prediction of High Tunnel Magnetoresistance Ratios in (111)-Oriented Junctions with SrTiO3 Barriers","Prediction of High Tunnel Magnetoresistance Ratios in (111)-Oriented Junctions with SrTiO3 Barriers","増田 啓介, 伊藤博介, 園部義明, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 伊藤博介, 園部義明, 介川 裕章, 三谷 誠司, 三浦 良雄","Intermag 2023","Intermag 2023","2023-05-15","","eng","oral_presentation","","","","","","We theoretically study the tunnel magnetoresistance (TMR) effect in novel (111)-oriented magnetic tunnel junctions (MTJs) with SrTiO3 barriers X/SrTiO3/X(111) (X = Co, Ni). Our ballistic transport calculation combining the density-functional theory and the Landauder formula obtains high TMR ratios of ∼500% for the Co-based MTJ and ∼300% for the Ni-based MTJ. By analyzing band structures in each region of the MTJs, we find that the high TMR ratios originate from the coherent tunneling of the half-metallic Λ1 state in Co (Ni), where the Λ1 state is the rotationally symmetric electronic state along the Λ line corresponding to the [111] direction. Since the in-plane lattice periodicity of SrTiO3 is twice as long as that of fcc Co (Ni), the original band structures of Co (Ni) are folded in the kx-ky plane, leading to the half-metallicity in the Λ1 state. The band-folding-driven high TMR ratios found in this study is a novel mechanism of high TMR ratios in (111)-oriented MTJs, in sharp contrast to the interfacial-resonance mechanism reported in our previous works.","" "Frontier of giant tunnel magnetoresistance effect for future spintronic applications","Frontier of giant tunnel magnetoresistance effect for future spintronic applications","介川 裕章","介川 裕章","The 1st Y-KAST International Conference","The 1st Y-KAST International Conference","2023-03-30","","eng","oral_presentation","","","","","","韓国において若手研究者が多く参加するThe 1st Y-KAST International Conferenceにおいてトンネル磁気抵抗素子の基礎と、NIMSにおける最先端素子の研究開発について招待講演を行う。","" "Highly efficient data acquisition and multilayer structure optimization of in-plane spin-valve-type CoFeB/MgO/CoFeB magnetic tunnel junctions","面内スピンバルブ型CoFeB/MgO/CoFeB 強磁性トンネル接合における高効率データ取得と多層構造最適化","介川 裕章, シャイケ トーマス, 温 振超, 葛西 伸哉, 三谷 誠司","介川 裕章, シャイケ トーマス, 温 振超, 葛西 伸哉, 三谷 誠司","第70回応用物理学会春季学術講演会","第70回応用物理学会春季学術講演会","2023-03-15","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)は磁気メモリ(MRAM)セルや高感度磁気センサーなどのスピントロニクス応用を担う中核的な素子である。トンネル磁気抵抗(TMR)比の大きさがMTJ における応用上の重要な性能の一つであるがその向上は長らく停滞していた。最近我々は単結晶MTJ を用いてバリア界面の最適化により大幅なTMR 比向上を報告した。本研究ではこの単結晶MTJ技術を応用素子で主流のCoFeB/MgO/CoFeB 型多結晶MTJ への展開を検討した。複雑な多層膜構造の高速プロセス最適化のため、自動基板搬送、自動傾斜膜成膜形成、反射高速電子回折(RHEED)取得などの機能を持つ高スループット成膜装置を活用し、ピン層を持つスピンバルブCoFeB/MgO/CoFeB 型MTJ のTMR 最適化を行った結果を報告する。" "Large tunnel magnetoresistance in (111)-oriented junctions with a SrTiO3 barrier","SrTiO3バリアを用いた(111)配向接合における大きなトンネル磁気抵抗効果","増田 啓介, 伊藤博介, 園部義明, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 伊藤博介, 園部義明, 介川 裕章, 三谷 誠司, 三浦 良雄","第70回応用物理学会春季学術講演会","第70回応用物理学会春季学術講演会","2023-03-15","","eng","oral_presentation","","","","","","We theoretically investigate the TMR effect in novel (111)-oriented magnetic tunnel junctions (MTJs) with a SrTiO3 barrier, X/SrTiO3/X(111) (X = Co, Ni). On the basis of the ballistic transport theory, we calculate TMR ratios by using the first-principles calculation and the Landauer formula. It is found that both MTJs have high TMR ratios of ~ 500% for the Co-based MTJ and ~ 300% for the Ni-based MTJ. The underlying mechanism of the high TMR ratios will be clarified.","" "Staircase-like tunnel resistance increase with barrier thickness in epitaxial Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","Staircase-like tunnel resistance increase with barrier thickness in epitaxial Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","シャイケ トーマス, 温 振超, 葛西 伸哉, 介川 裕章, 三谷 誠司","シャイケ トーマス, 温 振超, 葛西 伸哉, 介川 裕章, 三谷 誠司","第70回応用物理学会春季学術講演会","第70回応用物理学会春季学術講演会","2023-03-15","","eng","oral_presentation","","","","","","Magnetic tunnel junctions (MTJs) are essential for spintronics applications and, thus, have been extensively studied experimentally and theoretically. While, in general the concept of giant tunneling magnetoresistance (TMR) effect is understood by the so-called coherent tunneling mechanism, some transport phenomena of MTJs have yet to be clarified. One is the significant TMR oscillation with barrier thickness observed even at room temperature (RT) in high quality MTJs with a period of ~0.3 nm. Absent in most theoretical calculations, we aim to give further experimental inside on the behavior of the oscillations of recently reported Fe/wedged Mg4Al-Ox/Fe with peak RT TMR >400%. For this, we measured an array of over 450 MTJs on the same wafer and report Lorentz-like oscillation components in tunnel resistances at RT.","" "Fcc(111) epitaxial magnetic tunnel junctions with a Co90Fe10/Mg-Al-O/Co90Fe10 structure","Fcc(111) epitaxial magnetic tunnel junctions with a Co90Fe10/Mg-Al-O/Co90Fe10 structure","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","2022年第83回応用物理学会秋季学術講演会","2022年第83回応用物理学会秋季学術講演会","2022-09-20","","eng","oral_presentation","","","","","","The development of magnetic tunnel junctions (MTJs) with large tunnel magnetoresistance (TMR) is indispensable for creating next generation spintronic devices such as ultra-high density magnetoresistive random access memory (MRAM). Conventionally, bcc(001)-type MTJs are developed with relativerelatively large TMR value due to the delta1 preferential coherent tunneling mechanism (e.g., Fe/MgO/Fe(001)-type). Besides this, there are few reports on other epitaxial MTJ structures as large TMR candidates. Recent theoretical calculations predict that the fcc(111)-type MTJs with Co or Co-based alloy such as L11-CoPt and MgO barrier show a TMR ratio over 2000%, due to a new mechanism called interface resonant tunneling effect. In this work, we report the first TMR observation of this novel structure by preparing fully epitaxial fcc(111)-type MTJs with a Co90Fe10/Mg-Al-O (MAO) barrier/Co90Fe10(111) structure. ","" "Giant Tunnel Magnetoresistance at Room Temperature: Recent Progress and Prospect","Giant Tunnel Magnetoresistance at Room Temperature: Recent Progress and Prospect","介川 裕章","介川 裕章","The 6th Symposium for the Core Research Clusters for Materials Science and Spintronics, and The 5th Symposium on International Joint Graduated Program in Materials Science","The 6th Symposium for the Core Research Clusters for Materials Science and Spintronics, and The 5th Symposium on International Joint Graduated Program in Materials Science","2022-10-24","","eng","oral_presentation","","","","","","I will demonstrate significant TMR improvements by introducing advanced thin-film fabrication processes and a new MgAl2O4 spinel-based barrier material. The author’s group recently reported significant improvement in a TMR ratio of an Fe/MgO/Fe(001) through fine-tuning of Fe/MgO interface states: 417% at RT (914% at LT), which is almost twice (three times) as large as previous Fe/MgO/Fe reports. Further improvement was achieved using an Mg-rich spinel barrier, i.e., Fe/Mg4Al-Ox/Fe(001): 429% at RT and 1034% at LT. The LT-TMR ratio demonstrates a typical theoretical value in Fe/MgO/Fe. MgAl2O4-based barrier is beneficial to reduce the lattice-mismatch at the barrier interfaces, effectively suppressing atomic defects at both bottom and top side interfaces. These results indicate that there are enough room for enhancing TMR ratios in practical MTJs through fabrication process and material development. Recent progress of MgAl2O4-based MTJs is significant and further improvement can be expected in the near future. The giant TMR effect may widen the application range of spintronics, such as storage-class MRAMs and spintronic artificial intelligent devices. ","" "Generating process of magnon Bose-Einstein condensation in cubic anisotropic materials","立方異方性材料を用いたマグノン量子凝縮の生成過程の研究","小田鴻志, シャイケ トーマス, 介川 裕章, 関口康爾","小田鴻志, シャイケ トーマス, 介川 裕章, 関口康爾","2022年第83回応用物理学会秋季学術講演会","2022年第83回応用物理学会秋季学術講演会","2022-09-20","","jpn","oral_presentation","","","","","","","スピン波を用いた情報処理は、マグノン(スピン波を量子化した準粒子)の特徴的な性質によって、新しい技術をデバイスへ応用することが期待され、その一つにマグノン量子凝縮(マグノンBose-Einstein 凝縮)が挙げられる。マグノンは、超伝導と同じ巨視的量子現象であるBose-Einstein 凝縮を室温・大気圧中で生じることができ、極低温環境という制約に縛られている量子コンピュータ技術に新しい展開をもたらす可能性がある。我々は、熱安定性の高い材料を用いたマグノンBEC の観測を目的とし、室温下で従来材料であるイットリウム鉄ガーネットの11 倍以上の磁化を有する鉄単結晶を磁性材料として選択した2)。マグノン量子凝縮はパラメトリック励起と呼ばれるマグノンの励起手法が用いられるが、立方異方性を有する鉄単結晶では従来のパラメトリック励起が理解されていない。本講演では、鉄単結晶中にパラメトリック励起したマグノンを時間分解ブリルアン散乱分光法(BLS)を用いて解析し、立方異方性材料におけるパラメトリックマグノン生成について報告する。" "Large magnetocapacitance beyond 420% in epitaxial magnetic tunnel junctions with an MgAl2O4 barrier","Large magnetocapacitance beyond 420% in epitaxial magnetic tunnel junctions with an MgAl2O4 barrier","Kenta Sato, 介川 裕章, Kentaro Ogata, Gang Xiao, Hideo Kaiju","Kenta Sato, 介川 裕章, Kentaro Ogata, Gang Xiao, Hideo Kaiju","2022年第83回応用物理学会秋季学術講演会","2022年第83回応用物理学会秋季学術講演会","2022-09-20","","jpn","oral_presentation","","","","","","","Tunnel magnetocapacitance (TMC) effect in magnetic tunnel junctions (MTJs) has received increasing attention due to its interesting physics and the prospect of applications, such as hard disk drive and highly sensitive magnetic sensors. Recently, by optimizing appropriate frequencies and bias voltages, a large TMC of 332% was achieved in MgO-based MTJs at room temperature. However, the lattice-mismatch between MgO and Fe prevents further improvement in the properties of MgO-based MTJs. An alternative barrier, a cation-disordered spinel MgAl2O4 (MAO), is a good candidate for MTJs. The crystalline MAO barrier is superior to MgO in in-plane lattice matching with Fe. Therefore, a giant TMC beyond conventional values could be observed in MAO-based MTJs. In this work, we report the largest TMC of 426% in MTJs with cation-disordered spinel MAO barriers at room temperature." "Development of fcc-Co90Fe10/MgAlO/Co90Fe10(111) fully epitaxial magnetic tunnel junctions","fcc-Co90Fe10/MgAlO/Co90Fe10(111)フルエピタキシャル強磁性トンネル接合の開発","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","ソン ジェユアン, シャイケ トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","第46回日本磁気学会学術講演会","第46回日本磁気学会学術講演会","2022-09-06","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)を用いた新規応用デバイスの創生、例えば超高密度磁気ランダムアクセスメモ リや超高感度磁気センサーの実現など、には現在よりも大きなトンネル磁気抵抗(TMR)の実現が不可欠で ある。現在のMTJ のほとんどは、Fe/MgO/Fe やCoFeB/MgO/CoFeB に代表されるbcc(001)積層型であり、Δ1バンド優先コヒーレントトンネル機構によるTMR 効果が用いられている。最近第一原理計算によって、 fcc(111)型積層を持つCo/MgO/Co(111)やL11-CoPt/MgO/CoPt(111)構造において、従来とは異なる界面共鳴メカニズムによって大きなTMR 比(~2000%)が得られる可能性が予測されている。本研究ではfcc 構造が安定に得られるCo90Fe10 を磁性層に用い、Co90Fe10/Mg-Al-O(MAO)/Co90Fe10(111)型のフルエピタキシャルMTJを開発しTMR 効果が観測されたことを報告する。" "Fe/MgAlO/Fe(001)単結晶トンネル接合における巨大トンネル磁気抵抗効果","Fe/MgAlO/Fe(001)単結晶トンネル接合における巨大トンネル磁気抵抗効果","介川 裕章, シャイケ トーマス, 温 振超, 葛西 伸哉, 三谷 誠司","介川 裕章, シャイケ トーマス, 温 振超, 葛西 伸哉, 三谷 誠司","第46回日本磁気学会学術講演会","第46回日本磁気学会学術講演会","2022-09-06","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)はハードディスク読み取りヘッドや磁気ランダムアクセスメモリの記録ビット などスピントロニクス応用の中核となる素子である。しかし、現状では実用に用いることができるトンネル 磁気抵抗比(TMR 比)は200~300%以下であり、応用の幅を広げるためにはTMR 比の巨大化が必要である。最近、我々はFe/MgO/Fe(001)の従来型MTJ においても、界面構造の改善によって大幅にTMR 増大が可能であり、室温400%以上のTMR 比が得られることを報告した。しかしMgO とFe との格子不整合により界面構造のさらなる構造改善は困難とわかった。このため本研究ではより格子整合性がよいスピネルバリアに着目した。Mg リッチ組成のMg4Al-Ox(MAO)をバリアとしたFe/MAO/Fe(001)素子を開発することでTMR比の増大が観察されたこと、TMR 比のバリア膜厚に対する振動の振幅にも増大がみられたことを報告する。またTMR 振動の精密なデータ取得のため多数の微細加工素子を用いたデータ収集を行った。" "Giant tunnel magnetoresistance of 429% at 300 K and 1,034% at 10 K in Fe/Mg-rich Mg-Al-O/Fe(001) junctions","Giant tunnel magnetoresistance of 429% at 300 K and 1,034% at 10 K in Fe/Mg-rich Mg-Al-O/Fe(001) junctions","介川 裕章, シャイケ トーマス, 温 振超, 三谷 誠司","介川 裕章, シャイケ トーマス, 温 振超, 三谷 誠司","24th International Colloquium on Magnetic Films and Surfaces (ICMFS-2022)","24th International Colloquium on Magnetic Films and Surfaces (ICMFS-2022)","2022-07-10","","eng","oral_presentation","","","","","","The tunnel magnetoresistance (TMR) effect in magnetic tunnel junctions (MTJs) has been established as the heart of spintronic applications such as read heads of hard disk drives and magnetoresistive random access memories (MRAMs). Improvement in TMR ratios is indispensable for developing novel spintronic applications. However, TMR ratios at room temperature (RT) remain around 300% or less even for state-of-the-art CoFeB/MgO/CoFeB based MTJs. Recently, we reported significant improvement in TMR ratios of a conventional MTJ with a Fe/MgO/Fe(001) structure by MgO interface modifications: 417% at RT (914% at 5 K) being almost twice (three times) as large as the typical ratios in Fe/MgO/Fe reports. However, we observed many misfit dislocations at the Fe/MgO interfaces, limiting further improvement in TMR ratios. In this study, we developed a Mg-rich spinel-based barrier, Mg4Al-Ox to suppress the mismatch problem for enhancing the TMR ratio of a Fe-based MTJ.","" "Fcc(111) epitaxial magnetic tunnel junctions with a Co90Fe10/Mg-Al-O/Co90Fe10 structure","Fcc(111) epitaxial magnetic tunnel junctions with a Co90Fe10/Mg-Al-O/Co90Fe10 structure","ソン ジェユアン, シェーク トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","ソン ジェユアン, シェーク トーマス, ハ ツォン, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","2022年第69回応用物理学会春季学術講演会","2022年第69回応用物理学会春季学術講演会","2022-03-22","","eng","oral_presentation","","","","","","The development of magnetic tunnel junctions (MTJs) with large tunnel magnetoresistance (TMR) is indispensable for creating next generation spintronic devices. To exceed the values in conventional bcc(001)-type MTJs that use a 1 preferential coherent tunneling mechanism (e.g., Fe/MgO/Fe(001)-type), a new MTJ stack structure should be explored. Recent theoretical calculations predicts that the fcc(111)-based MTJs including pure Co and L11-type ferromagnetic layers show a TMR ratio over 2000% due to the interface resonant tunneling effect. In this work, we report the first TMR observation by preparing fully epitaxial fcc(111) type MTJs with a Co90Fe10/Mg-Al-O (MAO) barrier/Co90Fe10(111) structure. ","" "Giant tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","Giant tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","シェーク トーマス, 温 振超, 介川 裕章, 三谷 誠司","シェーク トーマス, 温 振超, 介川 裕章, 三谷 誠司","2022年第69回応用物理学会春季学術講演会 https://meeting.jsap.or.jp/","2022年第69回応用物理学会春季学術講演会 https://meeting.jsap.or.jp/","2022-03-22","","eng","oral_presentation","","","","","","Tunnel magnetoresistance (TMR) is one of the most important properties for magnetic tunnel junction (MTJ) based devices such as magnetoresistive memories. Recently, we demonstrated significantly large TMR ratios using a conventional Fe/MgO/Fe(001) MTJ structure; 417% at room temperature (RT) (914% at 5 K) is almost twice (three times) as large as the typical ratios in Fe/MgO/Fe reports. The improvement was attributed to the development of MgO interface modification technology, such as post-oxidation. However, due to the large lattice mismatch between Fe and MgO, many misfit dislocations are introduced at their interfaces, which limits further improvement of the TMR ratio. In this study, we report enhanced TMR ratios using a Mg-rich spinel barrier, Mg4Al-Ox.","" "Electrical Detection of Backward Spin-waves in Epitaxial Fe Films","Electrical Detection of Backward Spin-waves in Epitaxial Fe Films","S. Nezu, シェーク トーマス, 介川 裕章, K. Sekiguchi","S. Nezu, シェーク トーマス, 介川 裕章, K. Sekiguchi","2022 Joint MMM-INTERMAG conference","2022 Joint MMM-INTERMAG conference","2022-01-10","","eng","oral_presentation","","","","","","Magnonics has many advantages in performing logic and nonlinear signal processing with low with low-power consumption. However, the propagation loss of spin waves prevents a practical application of spin waves. Recently, cubic anisotropy materials were reported to be a promising spin-wave medium, because the surface spin-wave minimizes its resonant frequency due to the anisotropic magnetic field. The amplitude, group velocity, and decay length were greatly enhanced, enough to be at a practical application level. In this study, we investigated the electrical detection of backward spin-waves in cubic anisotropic Fe films, which is essential to fabricating two dimensional magnonic devices and has not been reported so far.","" "Giant tunnel magnetoresistance ratio and oscillation in Fe/MgO/Fe(001) and Fe/MgAlO/Fe(001) magnetic tunnel junctions","Giant tunnel magnetoresistance ratio and oscillation in Fe/MgO/Fe(001) and Fe/MgAlO/Fe(001) magnetic tunnel junctions","シェーク トーマス, 介川 裕章, 向 清懿, 温 振超, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 向 清懿, 温 振超, 大久保 忠勝, 宝野 和博, 三谷 誠司","2022 Joint MMM-INTERMAG conference","2022 Joint MMM-INTERMAG conference","2022-01-10","","eng","oral_presentation","","","","","","A magnetic tunnel junction (MTJ) is one of the most important device structures in spintronic applications. However, significant improvement in the tunnel magnetoresistance (TMR) ratio at room temperature (RT) is necessary to establish novel spintronic applications. Even in a simple Fe/MgO/Fe(001) MTJ, the experimental TMR ratios (180-220% at RT) are much smaller than the theoretical values >1,000%. In addition, the origin of TMR oscillation with the barrier thickness in experiments is still an open question. In this study, we revisited Fe/MgO/Fe(001) based structures to bridge the discrepancies between experiments and theories. We deposited Fe/MgO/Fe(001) MTJs on a Cr-buffered MgO(001) single crystal substrate. By combining sputtering and electron-beam evaporation, we improved the barrier interface crystallinity. We further examined an MgAl2O4 (MAO) based barrier to reduce the lattice mismatch with Fe. An MAO composition of Mg:Al = 4:1 (Mg rich) was selected.","" "Effect of Counter Electrode on Tunneling Anisotropic Magnetoresistance through Iron Quantum Wells","Effect of Counter Electrode on Tunneling Anisotropic Magnetoresistance through Iron Quantum Wells","アルマハドウイ ミフタ, 向 清懿, 三浦 良雄, ベルムバーリク モハメド, 増田 啓介, 葛西 伸哉, 介川 裕章, 三谷 誠司","アルマハドウイ ミフタ, 向 清懿, 三浦 良雄, ベルムバーリク モハメド, 増田 啓介, 葛西 伸哉, 介川 裕章, 三谷 誠司","2022 Joint MMM-INTERMAG conference","2022 Joint MMM-INTERMAG conference","2022-01-10","","eng","oral_presentation","","","","","","Utilization of quantum transport is of interest for exploring new functionalities in magnetic tunnel junctions (MTJs). In a recent Letter, we showed an anisotropy in resonant tunneling conduction through Fe quantum wells (QWs) in MTJs, with a lattice-matched (001)-oriented stack of: Cr/Fe-QW/MgAlO. The QW confinement is selected for Δ1-symmetry states by the band-symmetry mismatch between Fe and Cr. We obtained a large tunneling anisotropic magneto-resistance of QWs (QWTAMR) up to 5%. In this work, we experimentally analyze the symmetry of the resonant tunneling conduction states and QW-TAMR. We compare the effect of the counter electrode (X), where we chose three materials having a different Δ1 band edge level; single-crystal Fe, amorphous CoFeB, and single-crystal Cr.","" "Magnetization switching induced by spin–orbit torque from Co2MnGa magnetic Weyl semimetal thin films","Magnetization switching induced by spin–orbit torque from Co2MnGa magnetic Weyl semimetal thin films","唐 柯, 温 振超, Yong-Chang Lau, 介川 裕章, Takeshi Seki, 三谷 誠司","唐 柯, 温 振超, Yong-Chang Lau, 介川 裕章, Takeshi Seki, 三谷 誠司","日本電子材料協会2021年度第58回秋期講演大会","日本電子材料協会2021年度第58回秋期講演大会","2021-11-25","","eng","oral_presentation","","","","","","In this work, the spin current generation and spin-orbit torque(SOT)-driven magnetization switching in Co2MnGa-based MWS thin films were studied. The Co2MnGa (001) films epitaxially grown on MgO (001) substrates show flat surface morphology and highly B2-ordered structures. The spin Hall efficiency ξ_SH of Co2MnGa was estimated to be -7.8% in a SOT device with the core structure of Co2MnGa(1.3 nm)/Ti (3 nm)/CoFeB(1.1 nm). In the same device, the SOT-driven magnetization switching of the perpendicularly magnetized CoFeB layer was demonstrated. According to the Hall resistance, almost all the magnetic moments of the CoFeB film were reversed by the applied electrical current. Then the mechanisms of the spin current generation in this trilayer structure were studied. The amplitude of ξ_SH slightly decreases with increasing t. The second harmonic Hall signal shows a non-zero value when the magnetization of Co2MnGa and the electrical field are collinear. The anomalous Hall effect loops show negligible shifts over applied currents. The above results indicate that the spin-orbit filtering effect at the Co2MnGa/Ti interface and/or magnetization-independent spin Hall effect in Co2MnGa may be responsible for the spin current generation in the Co2MnGa/Ti/CoFeB heterostructure.","" "Design of MgAl2O4 Spinel-Oxide-Based Tunnel Barriers for Advanced Spintronics Devices","Design of MgAl2O4 Spinel-Oxide-Based Tunnel Barriers for Advanced Spintronics Devices","名和 憲嗣, 増田 啓介, 市川 心人, 介川 裕章, 鈴木 健司, 中田勝之, 三谷 誠司, 三浦 良雄","名和 憲嗣, 増田 啓介, 市川 心人, 介川 裕章, 鈴木 健司, 中田勝之, 三谷 誠司, 三浦 良雄","KMS 2021 Winter Conference","KMS 2021 Winter Conference","2021-11-24","","eng","oral_presentation","","","","","","We performed ballistic-conductance calculations in an Fe/MgO(n)/MgAl2O4/MgO(n)/Fe(001) MTJ using the non-equilibrium Green’s functions method to clarify the TMR ratio under bias voltage application. Here, number of MgO layers (n-ML) is changed as n = 1, 2, 3. In the case of n = 1, a large TMR ratio of 1184% is obtained at a zero-bias voltage and this large value is almost maintained up to V = 1.2 V, leading to a large voltage output. In contrast, a single barrier MgAl2O4 shows only a small TMR ratio (~125%), which is constant below V = 1.6 V. These results indicate that both the models have a similar tendency in bias voltage dependence of TMR, except for the magnitude of a TMR ratio. Moreover, we clarified that the presence of an MgO interlayer between Fe and MgAl2O4 plays an important role in retaining (blocking) the ∆1 evanescent state for majority (minority) spin. The former leads to the robustness of the TMR ratio against bias voltage as observed in single MgAl2O4 MTJs, while the latter does to the large TMR ratio as in single MgO MTJs.","" "Theoretical Prediction of Giant Tunnel Magnetoresistance and Large Perpendicular Magnetic Anisotropy in Unconventional (111)-Oriented Magnetic Tunnel Junctions","Theoretical Prediction of Giant Tunnel Magnetoresistance and Large Perpendicular Magnetic Anisotropy in Unconventional (111)-Oriented Magnetic Tunnel Junctions","増田 啓介, 伊藤博介, 園部 義明, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 伊藤博介, 園部 義明, 介川 裕章, 三谷 誠司, 三浦 良雄","The 5th Symposium for The Core Research Clusters for Materials Science and Spintronics, and the 4th Symposium on International Joint Graduate Program in Materials Science","The 5th Symposium for The Core Research Clusters for Materials Science and Spintronics, and the 4th Symposium on International Joint Graduate Program in Materials Science","2021-10-25","","eng","oral_presentation","","","","","","In this work, we theoretically investigate the possibility of unconventional (111)-oriented MTJs with L11-ordered fcc ferromagnetic alloys (Fig. 1) for achieving both high TMR ratios and large PMA. Since the (111) plane is the close-packed plane of the fcc lattice and has the lowest surface energy, it is natural to consider (111)-oriented MTJs when fcc ferromagnets are used as the electrodes. By constructing various supercells with an MgO tunnel barrier and different L11 alloys, we calculated their TMR ratios on the basis of the density-functional theory and the Landauer formula. We found that the MTJs with Co-based L11 alloys (CoNi, CoPt, and CoPd) show giant TMR ratios over 2000%. Through the comparison of the wave-vector-resolved conductance and the local density of states, we concluded that the giant TMR ratios are attributed to the resonant tunneling of the interfacial antibonding between Co d and O p states. Magnetic anisotropies in these MTJs were also calculated and relatively large PMA in bulk L11 alloys was obtained [1]. From these results, we propose that the present (111)-oriented MTJs are strong candidates for achieving high TMR ratios and large PMA.","" "Giant tunnel magnetoresistance and perpendicular magnetic anisotropy in (111)-oriented magnetic tunnel junctions with L11-ordered ferromagnetic alloys","Giant tunnel magnetoresistance and perpendicular magnetic anisotropy in (111)-oriented magnetic tunnel junctions with L11-ordered ferromagnetic alloys","増田 啓介, 伊藤博介, 園部 義明, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 伊藤博介, 園部 義明, 介川 裕章, 三谷 誠司, 三浦 良雄","第82回応用物理学会秋季学術講演会","第82回応用物理学会秋季学術講演会","2021-09-10","","eng","oral_presentation","","","","","","We theoreticaly studied the tunnel magnetoresistance (TMR) effect and magnetic anisotropy in unconventional (111)-oriented magnetic tunnel junctions (MTJs) with L11-ordered ferromagnetic alloys. We estimated the TMR ratios and magnetic anisotropy energies by using the first-principles calculations and found that the MTJs with Co-based L11 alloys have both high TMR ratios and large perpendicular magnetic anisotropies (PMA). In this talk, we will show the detailed calculation results and discuss the underlying mechanism for the obtained high TMR ratios and large PMA.","" "Fe/MgO/Fe(001): Observation of tunnel magnetoresistance exceeding 400% at room temperature and 900% at low temperature","Fe/MgO/Fe(001):室温400%・低温900%を超えるトンネル磁気抵抗比の観測","シェーク トーマス, 向 清懿, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 向 清懿, 温 振超, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","第45回 日本磁気学会学術講演会 https://www.magnetics.jp/kouenkai/2021/","第45回 日本磁気学会学術講演会 https://www.magnetics.jp/kouenkai/2021/","2021-08-31","","jpn","oral_presentation","","","","","","","2004年にFe/MgO/Fe(001)構造の強磁性トンネル接合(MTJ)において室温180%の巨大トンネル磁気抵抗(TMR)効果が報告されたのち、スピントロニクス応用は飛躍的な進化を遂げた。それまでのアモルファスバリアを用いたMTJより数倍大きい値が容易に得られるようになり、素子電気出力増大の恩恵によって新デバイス創成に大きく寄与してきた。一方、理論計算によるとFe/MgO/Feは1,000%を優に超えるTMR比が予測されており、室温180~220%(低温290~370%)の実験値とは大きな乖離がある。本研究ではその理由の一端を明らかにするためFe/MgO/Feに改めて着目した。単結晶成長法の改善の結果、素子の高品質化を達成し、室温で400%以上、低温では理論値に迫る900%を超える非常に大きな値が得られたので報告する。" "Theoretical study for unconventional (111)-oriented magnetic tunnel junctions","(111)配向磁気トンネル接合の理論研究","増田 啓介, 伊藤博介, 園部 義明, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 伊藤博介, 園部 義明, 介川 裕章, 三谷 誠司, 三浦 良雄","第45回 日本磁気学会学術講演会","第45回 日本磁気学会学術講演会","2021-08-31","","jpn","oral_presentation","","","","","","","これまで行ってきた新規(111)配向磁気トンネル接合における磁気抵抗(TMR)効果、磁気異方性の理論研究結果について報告する。まずfcc-Co/MgO/fcc-Co(111)で巨大なTMR比が得られることを示し、強磁性電極をCo系のL11合金に変えることで巨大なTMR比に加え大きな垂直磁気異方性も得られることについて言及する。" "Dielectric breakdown characteristics of lattice-matched MgAl2O4-based magnetic tunnel junctions","格子整合MgAl2O4バリアトンネル磁気抵抗素子の絶縁破壊特性","介川 裕章, 温 振超, 葛西 伸哉, クマール アシュトッシュ, 大久保 忠勝, 宝野 和博, 三谷 誠司, 市川心人, 中田勝之","介川 裕章, 温 振超, 葛西 伸哉, クマール アシュトッシュ, 大久保 忠勝, 宝野 和博, 三谷 誠司, 市川心人, 中田勝之","第45回 日本磁気学会学術講演会","第45回 日本磁気学会学術講演会","2021-08-31","","jpn","oral_presentation","","","","","","","スピントルク駆動型磁気メモリ(STT-MRAM)などの応用では高い絶縁破壊耐電圧を持つ強磁性トンネル接合(MTJ)の実現が望まれる。MTJバリア層としてMgOが広く用いられているが、その膜厚は1 nm程度と非常に薄くその耐電圧の確保が大きな課題である。MTJの耐電圧はバリア層界面近傍の結晶品位や原子欠陥と密接に関係していることが知られている。CoFe(B)磁性層と格子不整合が非常に小さく、界面欠陥の抑制が容易なMgAl2O4スピネルバリアMTJでは比較的良好なTDDB(経時破壊)特性を持つことが報告されている。本研究ではMgAl2O4バリアMTJに着目し、その耐電圧について直流(DC)電圧及び10 ns程度の短パルス電圧を用いて詳細に検討した。この目的のため、数Ω・μm2程度の面積抵抗(RA)を持つ単結晶CoFe/MgAl2O4/CoFe(001)格子整合MTJを作製し、同等のトンネル磁気抵抗(TMR)比、RAを持つCoFe/MgO/CoFe参照試料と電圧破壊特性を比較した。" "Revisiting Fe/MgO/Fe(001): Giant tunnel magnetoresistance up to ~420% at room temperature","Revisiting Fe/MgO/Fe(001): Giant tunnel magnetoresistance up to ~420% at room temperature","介川 裕章, シェーク トーマス, 向 清懿, 温 振超, 大久保 忠勝, 宝野 和博, 三谷 誠司","介川 裕章, シェーク トーマス, 向 清懿, 温 振超, 大久保 忠勝, 宝野 和博, 三谷 誠司","The 32nd Magnetic Recording Conference (TMRC2021)","The 32nd Magnetic Recording Conference (TMRC2021)","2021-08-16","","eng","oral_presentation","","","","","","固体磁気メモリMRAMおよび高密度磁気記録に関するIEEE主催の国際学会、The 32nd Magnetic Recording Conference (TMRC2021)のMRAMセッションにおいて最新のFe/MgO/Fe型素子の研究成果について招待講演を行う。","" "トンネル磁気抵抗効果の新展開","トンネル磁気抵抗効果の新展開","介川 裕章","介川 裕章","電気学会、光・熱・電気との相互作用を活用した高機能磁気デバイス技術調査専門委員会 2021年度5月研究会 https://www.iee.jp/comite/a/ https://www.iee.jp/wp-content/uploads/honbu/16-pdf/AMAG1213s.pdf","電気学会、光・熱・電気との相互作用を活用した高機能磁気デバイス技術調査専門委員会 2021年度5月研究会 https://www.iee.jp/comite/a/ https://www.iee.jp/wp-content/uploads/honbu/16-pdf/AMAG1213s.pdf","2021-05-21","","jpn","oral_presentation","","","","","","","電気学会の専門委員会(光・熱・電気との相互作用を活用した高機能磁気デバイス技術調査専門委員会)の2021年度5月研究会にて最近のトンネル磁気抵抗効果に関連した成果や動向について招待講演を行う。特に、スピネルバリア素子、Fe/MgO/Fe型素子の進展や、量子井戸を介した新規現象、(111)方位新型素子について紹介を行う。" "Tunnel magnetoresistance sensors with CoFeBTa amorphous soft-magnetic sensing layer","Tunnel magnetoresistance sensors with CoFeBTa amorphous soft-magnetic sensing layer","中谷 友也, ラスリー コーダリー エルデソウキー マーモウド, 李 江南, セペリ アミン ホセイン, 介川 裕章, 桜庭 裕弥","中谷 友也, ラスリー コーダリー エルデソウキー マーモウド, 李 江南, セペリ アミン ホセイン, 介川 裕章, 桜庭 裕弥","INTERMAG 2021","INTERMAG 2021","2021-04-26","","eng","oral_presentation","","","","","","アモルファス軟磁性材料CoFeBTaを用いたトンネル磁気抵抗センサの、磁気抵抗および低周波ノイズを調べた。適切な熱処理により、線形性のよい磁界-抵抗応答特性が得られ、NiFeなど従来の軟磁性材料を用いた場合に比べ、低周波ノイズを半減することができた。このフルブリッジを作製し、10 Hzの周波数で500 pTの磁界分解能を得た。","" "磁気トンネル接合のトンネルバリア開発による巨大磁気抵抗の実現","磁気トンネル接合のトンネルバリア開発による巨大磁気抵抗の実現","介川 裕章","介川 裕章","2021年日本電子材料技術協会セミナー「磁気メモリの基礎と最前線」 https://www.jems1962.org/","2021年日本電子材料技術協会セミナー「磁気メモリの基礎と最前線」 https://www.jems1962.org/","2021-04-09","","jpn","oral_presentation","","","","","","","最近の強磁性トンネル接合の高トンネル磁気抵抗比の実現に関する研究成果や将来展望について日本電子材料技術協会セミナーにおいて招待講演を行う。" "Topological Weyl semimetal CoSi thin films with spin Hall effect enhanced by d-p orbital hybridization","Topological Weyl semimetal CoSi thin films with spin Hall effect enhanced by d-p orbital hybridization","唐 柯, Yong-Chang Lau, 名和 憲嗣, 温 振超, 向 清懿, 介川 裕章, Takeshi Seki, 三浦 良雄, Koki Takanashi, 三谷 誠司","唐 柯, Yong-Chang Lau, 名和 憲嗣, 温 振超, 向 清懿, 介川 裕章, Takeshi Seki, 三浦 良雄, Koki Takanashi, 三谷 誠司","第44回 日本磁気学会学術講演会","第44回 日本磁気学会学術講演会","2020-12-14","","eng","oral_presentation","","","","","","We report on the B20-ordered CoSi thin films fabricated on sapphire c-plane substrates by magnetron sputtering and the spin Hall effect (SHE) of the CoSi thin films investigated via spin Hall magnetoresistance and harmonic Hall measurements in CoSi/CoFeB/MgO heterostructures. An enhancement of spin Hall efficiency is achieved in the CoSi thin film compared to that in the pure Co and Si. The first-principles calculations reveal that unexpectedly, a remarkable peak of spin Berry curvature due to the bonding between d(Co)-p(Si) orbitals appears not at but rather near the spin-1 chiral fermions. ","" "CoFeBTaアモルファス軟磁性層を用いたTMRセンサ","CoFeBTaアモルファス軟磁性層を用いたTMRセンサ","ラスリー コーダリー エルデソウキー マーモウド, 中谷 友也, 李 江南, セペリ アミン ホセイン, 介川 裕章, 桜庭 裕弥","ラスリー コーダリー エルデソウキー マーモウド, 中谷 友也, 李 江南, セペリ アミン ホセイン, 介川 裕章, 桜庭 裕弥","第44回日本磁気学会学術講演会","第44回日本磁気学会学術講演会","2020-12-14","","jpn","oral_presentation","","","","","","","CoFeBTaアモルファス軟磁性層を用いたトンネル磁気抵抗センサの、磁気抵抗およびノイズ特性について発表する。" "Perpendicular magnetic anisotropy of Fe/cubic CrO/MgO heterostructures","Fe/立方晶CrO/MgOヘテロ構造の垂直磁気異方性","飯田 裕希, 向 清懿, シェーク トーマス, 温 振超, 岡林潤, 大久保 忠勝, 宝野 和博, 介川 裕章, 三谷 誠司","飯田 裕希, 向 清懿, シェーク トーマス, 温 振超, 岡林潤, 大久保 忠勝, 宝野 和博, 介川 裕章, 三谷 誠司","第44回 日本磁気学会学術講演会 / https://magnetics.jp/kouenkai/2020/","第44回 日本磁気学会学術講演会 / https://magnetics.jp/kouenkai/2020/","2020-12-14","","eng","oral_presentation","","","","","","We investigated structure and magnetic properties of Cr/Fe/MgO heterostructures formed by a sputtering process and found the formation of rock-salt-type CrO at the Fe/MgO interface, which shows interface PMA energies of 1.55 mJ/m2.","" "Preparation of topological semimetal CoSi thin films for spin-orbit torque devices","Preparation of topological semimetal CoSi thin films for spin-orbit torque devices","唐 柯, 温 振超, 向 清懿, 介川 裕章, 三谷 誠司","唐 柯, 温 振超, 向 清懿, 介川 裕章, 三谷 誠司","第67回応用物理学会春季学術講演会","第67回応用物理学会春季学術講演会","2020-03-12","","eng","oral_presentation","","","","","","In this work, we prepared topological semimetal CoSi thin films and investigated the spin Hall effect in the films. Polycrystalline CoSi films were successfully fabricated on several substrates. By comparing the crystallinity and roughness, it is found that the sapphire C-plane substrate is the best for the growth of CoSi films. The RHEED and XRD patterns indicate all the CoSi films are polycrystalline. A relatively flat surface with the average roughness (Ra) of 0.77 nm was achieved for a 47-nm-thick CoSi film. The θ_SHE of CoSi was evaluated by measuring the spin Hall magnetoresistance in a CoSi(0-11 nm)/CoFeB(1 nm)/MgAlOx(2 nm) structure. A sizable θ_SHE of ~3.5% was achieved in the polycrystalline CoSi film, which is large for material systems without heavy metals. In comparison with the spin Hall angles in pure Co (~1%) and Si (0.01%), the enhancement of θ_SHE in the CoSi films suggests that the topological electronic structures of CoSi may play a significant role on the spin Hall effect. ","" "Recent progress of magnetoresistive devices for spintronics applications: next generation memories and sensors","Recent progress of magnetoresistive devices for spintronics applications: next generation memories and sensors","介川 裕章","介川 裕章","Recent trends in spin-based aplications","Recent trends in spin-based aplications","2019-12-19","","eng","oral_presentation","","","","","","横浜国立大学にて行われるスピントロニクスに関する国際ワークショップにて最近のスピントロニクス素子応用の現状と将来についてNIMSでの最新研究結果を交え招待講演を行う。","" "Dielectric breakdown of MgAl2O4 based magnetic tunnel junctions using DC and ns voltage pulses 10","Dielectric breakdown of MgAl2O4 based magnetic tunnel junctions using DC and ns voltage pulses 10","介川 裕章, 温 振超, Shinto Ichikawa, 葛西 伸哉, 三谷 誠司, Katsuyuki Nakada","介川 裕章, 温 振超, Shinto Ichikawa, 葛西 伸哉, 三谷 誠司, Katsuyuki Nakada","IEDM2019,Special MRAM poster session","IEDM2019,Special MRAM poster session","2019-12-07","","eng","oral_presentation","","","","","","Improving breakdown voltages of magnetic tunnel junctions (MTJs) is one of the most important issues for various spintronic applications such as spin-transfer torque type magnetoresistive random access memories (STT-MRAMs). Although most applications use MgO-based MTJs, it is very difficult to maintain a high breakdown voltage when the MgO thickness is less than 1 nm. Also, the effect of lattice mismatch with CoFeB electrodes is not negligible since introduced misfit dislocations work as electron trapping sites that significantly reduce the breakdown voltage. Use of a spinel MgAl2O4 (MAO) barrier provides perfectly lattice-matched interfaces with CoFeB, leading to elimination of misfit-driven breakdown by electric stress. Therefore, in this study, we focused on breakdown voltages of lattice-matched MAO-MTJs with resistance area (RA) values between 3 and 10 W×mm2 using DC and 10-ns voltage pulses. We prepared epitaxial CoFe/MAO/CoFe(001) MTJ stacks on an MgO(001) substrate using magnetron sputtering. An MAO barrier was formed using natural oxidation of Mg-Al. A tunnel magnetoresistance (TMR) ratio and RA were evaluated by current-in-plane technique (CIPT) to be 155% (220%) and 3.3 ohm um2 (7 ohm um2), respectively. Breakdown voltages were evaluated using ramping DC voltages and 10-ns voltage pulses after patterning into 200´100 nm2 scale junctions. We observed breakdown voltages of ~1.1 V by DC and ~1.5 V by 10-ns pulses for MTJs with 3.3 ohm um2.","" "High-quality MgAl2O4-based magnetic tunnel junctions prepared by reactive sputtering method","反応性スパッタ法による高品位MgAl2O4バリア強磁性トンネル接合","市川 心人, 中田 勝之, 徐 先東, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","市川 心人, 中田 勝之, 徐 先東, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","第43回日本磁気学会学術講演会","第43回日本磁気学会学術講演会","2019-09-25","","jpn","oral_presentation","","","","","","","MgAl2O4(MAO)はスピネル構造を有する立方晶の酸化物として知られ、強磁性トンネル接合(MTJ)のトンネルバリアとして用いることで、近年室温において300%を超える大きなトンネル磁気抵抗(TMR)比が報告されている。また、MAO-MTJはCoFe系強磁性金属との格子整合性が良く高品位の界面構造を容易に実現できる為、良好なTMR比のバイアス電圧依存性(高Vhalf値)が得られ、それによって高い素子出力が得られるという応用上の利点がある。MAOトンネルバリア層の作製方法として、金属層の後酸化法、および焼結MAOターゲットの直接高周波スパッタリングが報告されているが、前者はバリア界面におけるラフネスの発生、後者は高い平坦性が得られるもののトンネルバリア層の酸化制御がより困難であるという課題がある。本研究では、平坦な界面と高い結晶性を備えた高品位なMAOトンネルバリア層を作製する新たな手法として、反応性スパッタリングを用いた手法を検討した。" "Lattice-matched magnetic tunnel junctions using a spinel barrier for advanced spintronics devices","Lattice-matched magnetic tunnel junctions using a spinel barrier for advanced spintronics devices","介川 裕章","介川 裕章","PRICM-10 ","PRICM-10 ","2019-08-18","","eng","oral_presentation","","","","","","3年に一度行われる金属研究に関する国際会議PRICM-10(Pacific Rim International Conference on Advanced Materials and Processing)において、スピネルバリアを有する強磁性トンネル接合の最新研究動向について招待講演を行う。","" "Reactive Sputtered Spinel MgAl2O4 Tunnel Barrier with Excellent Bias Voltage Dependence","Reactive Sputtered Spinel MgAl2O4 Tunnel Barrier with Excellent Bias Voltage Dependence","Katsuyuki Nakada, Shinto Ichikawa, 介川 裕章, 徐 先東, 大久保 忠勝, 宝野 和博, 三谷 誠司","Katsuyuki Nakada, Shinto Ichikawa, 介川 裕章, 徐 先東, 大久保 忠勝, 宝野 和博, 三谷 誠司","The 30th Magnetic Recording Conference (TMRC 2019)","The 30th Magnetic Recording Conference (TMRC 2019)","2019-07-08","","eng","oral_presentation","","","","","","磁気記録に関する国際学会、TMRC2019においてTDK共同研究の成果をポスター発表する。格子整合トンネル磁気抵抗素子に適したMgAl2O4系スピネルバリアを、従来手法の後酸化法、直接スパッタ法にかわり、酸素ガスを用いた反応性スパッタによる作製に成功した。反応性スパッタで作製されたスピネルバリア素子は、非常に広い抵抗領域で安定的な磁気抵抗特性を示し、とりわけ良好なバイアス電圧依存性を示したことから、産業上も有力な作製法となりうることがわかった。","" "Significant TMR oscillation effect in magnetic tunnel junctions with a MgAl2O4 barrier","Significant TMR oscillation effect in magnetic tunnel junctions with a MgAl2O4 barrier","介川 裕章, 三谷 誠司","介川 裕章, 三谷 誠司","York-Tohoku-Kaiserslautern Research Symposium on ""New-Concept Spintronics Devices""","York-Tohoku-Kaiserslautern Research Symposium on ""New-Concept Spintronics Devices""","2019-06-12","","eng","oral_presentation","","","","","","In this talk, we will introduce our recent experimental trials using a new epitaxial barrier, MgAl2O4 (spinel) to achieve better lattice-matching between Fe electrodes and a barrier. An Fe/MgAl2O4/Fe(001) MTJ structure can have lattice-matched and atomically-flat interfaces, enabling us to highlight the oscillation effect. We fabricated micrometer-size MTJs with a stack structure of MgO(001) substrate/Cr (40 nm)/Fe (100 nm)/MgAl2O4 (tMAO)/Fe (7 nm)/IrMn (12 nm)/Ru cap using a magnetron sputtering system. A wedge-shaped MgAl2O4 barrier was prepared by a linear motion shutter equipped with the sputtering system to evaluate tMAO dependences of a TMR ratio. A typical TMR ratio was 220% at 300 K (390% at 5 K).","" "MRAM 応用に向けた強磁性トンネル素子用新材料の開発","MRAM 応用に向けた強磁性トンネル素子用新材料の開発","介川 裕章","介川 裕章","新世代研究所2018年度第3回スピントロニクス研究会","新世代研究所2018年度第3回スピントロニクス研究会","2019-03-22","","jpn","oral_presentation","","","","","","","新世代研究所(ATI)スピントロニクス研究会、2018年度第3回スピントロニクス研究会(テーマ:「MRAM技術の新展開」)において、この数年NIMS で行ってきた単結晶素子ベースの時期トンネル接合用材料開発とその将来展望について概論する。" "Spin dependent transport in Co2FeAl/MgAl2O4/CoFe epitaxial magnetic tunnel junctions with and without CoFe insertion","Spin dependent transport in Co2FeAl/MgAl2O4/CoFe epitaxial magnetic tunnel junctions with and without CoFe insertion","シェーク トーマス, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","第66回応用物理学会春季学術講演会","第66回応用物理学会春季学術講演会","2019-03-09","","eng","oral_presentation","","","","","","For the application in magnetic random-access memory (MRAM) devices, magnetic tunnel junctions (MTJs) with large tunnel magnetoresistance (TMR) in combination with low junction resistance area product (RA) and small TMR-bias voltage dependence are desired. It is generally known that these features are significantly affected by the ferromagnet/barrier interfaces. Therefore, insertion of certain materials at the interfaces have shown to be useful in altering transport properties of MTJs. Previously, we have found an increase (strong decrease) of TMR (RA) by insertion of a thin CoFe layer in Co2FeAl/inserted CoFe (0 or 1 nm)/MgAl2O4/CoFe(001) MTJs. Here, we study the origin of the change by analyzing their microstructure and conductance temperature dependence.","" "High-quality MgAl2O4-based magnetic tunnel junctions prepared by two-step oxidation method","2回酸化法による高品位MgAl2O4バリア強磁性トンネル接合","市川 心人, ポ ハン チェン, 介川 裕章, 三谷 誠司, 大久保 忠勝, 宝野 和博, 中田勝之","市川 心人, ポ ハン チェン, 介川 裕章, 三谷 誠司, 大久保 忠勝, 宝野 和博, 中田勝之","第66回応用物理学会春季学術講演会","第66回応用物理学会春季学術講演会","2019-03-09","","jpn","oral_presentation","","","","","","","MgAl2O4(MAO)バリアを有する強磁性トンネル素子(MTJ)はCoFe系強磁性金属との格子整合性が良く高品位の界面構造を容易に実現できる為、良好なTMR比のバイアス電圧依存性が得られ、それによって高い素子出力が得られるという応用上の利点がある。MAO層の主要な作製方法として、Mg-Al合金膜を成膜し、その後酸化させる後酸化法が知られている。しかし、後酸化法は最適条件以外では不均一酸化や界面の過酸化が起こりやすく制御が難しい。例えば最適酸化条件が得られるMg-Al膜厚以外では急激にTMR比の低下が起こる。そこで本研究ではMAO作製を2回に分けて行う2回酸化法を導入し、MAO層の均質性改善による特性向上を狙った。" "High quality spinel MgAl O tunnel barrier grown by controlled reactive sputtering","High quality spinel MgAl O tunnel barrier grown by controlled reactive sputtering","Katsuyuki Nakada, Shinto Ichikawa, 徐 先東, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","Katsuyuki Nakada, Shinto Ichikawa, 徐 先東, 介川 裕章, 大久保 忠勝, 宝野 和博, 三谷 誠司","MMM-Intermag Joint Conference","MMM-Intermag Joint Conference","2019-01-14","","eng","oral_presentation","","","","","","In this work we explored an oxygen reactive sputtering to create a uniform MAO barrier with a high crystallinity. We prepared epitaxial Fe/MAO/Fe(001) MTJ stacks on an MgO(001) substrate using a magnetron sputtering system. An MAO barrier was formed using rf sputtering of Mg Al with Ar-O gas mixture at room temperature. Using an optimized oxidizing atmosphere during the deposition, atomically flat and compositionally uniform MAO barriers were successfully prepared for a wide range of barrier thicknesses. This work demonstrates that the reactive sputtering is a promising fabrication method for high performance MAO-based MTJs with good stability and reproducibility for various spintronic device application.","" "Strong modulation of finitebias tunnel magnetoresistance due to quantum well states in Cr/Fe/MgAl2O4/Fe(001) junctions","Strong modulation of finitebias tunnel magnetoresistance due to quantum well states in Cr/Fe/MgAl2O4/Fe(001) junctions","向 清懿, 介川 裕章, ベルムバーリク モハメド, アルマハドウイ ミフタ, シェーク トーマス, 葛西 伸哉, 三浦 良雄, 三谷 誠司","向 清懿, 介川 裕章, ベルムバーリク モハメド, アルマハドウイ ミフタ, シェーク トーマス, 葛西 伸哉, 三浦 良雄, 三谷 誠司","MMM-Intermag Joint Conference","MMM-Intermag Joint Conference","2019-01-14","","eng","oral_presentation","","","","","","In this study, Cr/ultrathinFe/MgAl2O4/Fe based magnetic tunnel junctions (MTJs) were prepared with exact ultrathin Fe monolayer number, n , i.e., the QW width. Associated with almost perfect lattice matching between Fe and MgAl2O4, the ultrathin Fe layer exhibited perfect interfaces to form QW. Hence, the Spindependent resonant tunneling (SDRT) effect dominates the coherent tunneling process with a strong modulation on TMR even at room temperature. Since the ultrathin Fe has perpendicular easy axis, an observed magnetoresistance (MR) is calculated with parallel (P) and perpendicular configurations of the two magnetizations, where antiparallel (AP) conductance and conventional MR (calculated with P and AP states) can be deduced. For a 5 monolayer (ML) Fe sample, the dI/dV spectrum shows clearly resonant peak structures for the P state, while weakened for the AP state at the resonant bias voltage (Vbias), at which the Δ1 channels are localized. Meanwhile, the MR is definitely larger at the resonant V than that at zero bias as peak structure. In addition, for the 6ML Fe case, the resonant V is near zero bias, which leads to an ~1.6 times larger zero bias TMR comparing to the 5ML Fe case.","" "Interfacial perpendicular magnetic anisotropy in Fe/MgAl2O4: A first-principles and experimental study","Interfacial perpendicular magnetic anisotropy in Fe/MgAl2O4: A first-principles and experimental study","増田 啓介, 向 清懿, 介川 裕章, 三谷 誠司, 三浦 良雄","増田 啓介, 向 清懿, 介川 裕章, 三谷 誠司, 三浦 良雄","2019 Joint MMM-Intermag Conference","2019 Joint MMM-Intermag Conference","2019-01-14","","eng","oral_presentation","","","","","","磁気ヘテロ接合Fe/MgAl2O4の界面における磁気異方性を第一原理計算を用いて解析した。その結果、良く知られたFe/MgOの界面と同様に、面直磁気異方性が得られた。2次摂動論を用いてこのような面直磁気異方性の起源について調べたところ、Fermi面付近のスピン保存電子散乱が主要な寄与を果たしていることがわかった。","" "Resonant tunneling anisotropic magnetoresistance in an Fe spin-dependent quantum well","Resonant tunneling anisotropic magnetoresistance in an Fe spin-dependent quantum well","アルマハドウイ ミフタ, 向 清懿, ベルムバーリク モハメド, 介川 裕章, 葛西 伸哉, 増田 啓介, 三浦 良雄, 三谷 誠司","アルマハドウイ ミフタ, 向 清懿, ベルムバーリク モハメド, 介川 裕章, 葛西 伸哉, 増田 啓介, 三浦 良雄, 三谷 誠司","MMM-Intermag Joint Conference","MMM-Intermag Joint Conference","2019-01-14","","eng","oral_presentation","","","","","","Cr/Fe/MgAl2O4量子井戸構造を有する強磁性トンネル接合における異方性トンネル磁気抵抗効果について報告する。共鳴状態において、異方性磁気抵抗効果が増大し、室温においても有限の大きさの効果が生じることを見出した。","" "Oscillatory dependence of both tunnel magnetoresistance and tunnel anisotropic magnetoresistance on the barrier thickness in Fe/MgAl2O4/Fe(001) junctions","Oscillatory dependence of both tunnel magnetoresistance and tunnel anisotropic magnetoresistance on the barrier thickness in Fe/MgAl2O4/Fe(001) junctions","ベルムバーリク モハメド, アルマハドウイ ミフタ, 介川 裕章, 三谷 誠司","ベルムバーリク モハメド, アルマハドウイ ミフタ, 介川 裕章, 三谷 誠司","MMM-Intermag Joint Conference","MMM-Intermag Joint Conference","2019-01-14","","eng","oral_presentation","","","","","","Fe/MgAl2O4/Fe(001) 構造を有する単結晶強磁性トンネル接合において明瞭なトンネル磁気抵抗比のMgAl2O4バリア膜厚による振動現象を確認した。さらに、トンネル異方性磁気抵抗効果もバリア膜厚に対して振動的振る舞いをする新たな現象も明らかにした。","" "アモルファス基板上に作製したMgAl2O4障壁を持つ格子整合トンネル磁気抵抗素子","アモルファス基板上に作製したMgAl2O4障壁を持つ格子整合トンネル磁気抵抗素子","介川 裕章","介川 裕章","平成30年度磁性材料研究会","平成30年度磁性材料研究会","2018-11-09","","jpn","oral_presentation","","","","","","","中性子産業利用推進協議会 平成30年度磁性材料研究会において、CoFeB/MgAl2O4/CoFeB型多結晶MTJに関して招待発表を行う。極薄MgO層を下部CoFeBとMg-Al-O層界面に挿入することで(001)成長した均一バリアが実現され、室温で240%を超える高いTMR比と良好なバイアス電圧依存性が得られ、従来の単結晶接合よりも大幅に実用的な構造が達成されたことなどを講演する。" "Recent progress of magnetic tunnel junctions with new spinel barrier materials","Recent progress of magnetic tunnel junctions with new spinel barrier materials","介川 裕章","介川 裕章","RIKEN-NIMS 第2 回 マテリアルイノベーションコア Workshop","RIKEN-NIMS 第2 回 マテリアルイノベーションコア Workshop","2018-11-06","","eng","oral_presentation","","","","","","RIKEN-NIMS 第2 回 マテリアルイノベーションコア Workshopにおいてスピネル系トンネルバリアを持つ強磁性トンネル素子の最近の進展について紹介を行った。","" "Large Perpendicular Magnetic Anisotropy in Fe-Al/MgAl2O4(001) epitaxial heterostructures","Large Perpendicular Magnetic Anisotropy in Fe-Al/MgAl2O4(001) epitaxial heterostructures","シェーク トーマス, 介川 裕章, 徐 先東, 三谷 誠司, 宝野 和博","シェーク トーマス, 介川 裕章, 徐 先東, 三谷 誠司, 宝野 和博","INTERMAG 2018","INTERMAG 2018","2018-04-23","","eng","oral_presentation","","","","","","Fe-Al合金はbcc構造を持つ強磁性体でありFe-Al組成によって磁気特性を調整できる。本研究では、FeAl層を超薄膜化してスピネルバリアと組み合わせることで非常に大きな垂直磁気異方性が得られたことを報告する。特に、Fe80Fe20組成において作製条件を最適化したCr/FeAl(0.8 nm)/MgAl2O4構造では、450℃のアニール後に磁気異方性エネルギKeff = 1.1 MJ/m3と非常に高い値が得られた。このことから、FeAl合金超薄膜が垂直磁化層として有望であることが期待される。","" "Control of magnetic anisotropy by lattice distortion in cobalt ferrite thin films","Control of magnetic anisotropy by lattice distortion in cobalt ferrite thin films","Hiroshige Onoda, 介川 裕章, Yanagihara Hideto","Hiroshige Onoda, 介川 裕章, Yanagihara Hideto","INTERMAG 2018","INTERMAG 2018","2018-04-23","","eng","oral_presentation","","","","","","Large perpendicular magnetic anisotropy (PMA) can be introduced via the magnetoelastic effects in a uniaxial distortion by a substrate-induced epitaxial strain, for example. In fact, cobalt-ferrite (CFO) thin films grown on an MgO (001) substrate suffering 0.6% in-plane tensile strain results in introducing a large PMA energy Ku of 14.7 Merg/cm3. Likewise, CFO films grown on MgAl2O4 (001) substrate suffering 3.6% in-plane compressive strain exhibits as large as negative Ku of – 60 Merg/cm3. Even though such large lattice strains, those induced PMA of CFO (001) epitaxial films can be quantitatively explained within a framework of magneto-elastic theory. In other words, the induced magnetic anisotropy can be quantitatively explained by the phenomenological magneto-elastic effect at least in this lattice distortion range. Based on this effect, further enhanced PMA by inducing 3~4% tensile strain can be expected. Therefore, in this study, we examined various buffer layers to introduce a larger lattice strain than MgO (001) and report the magnetic anisotropy (MA), especially induced Ku in CFO (001).","" "Development of all spinel magnetic tunnel junctions: epitaxial Fe3O4/MgAl2O4/Fe3O4(001) structure","Development of all spinel magnetic tunnel junctions: epitaxial Fe3O4/MgAl2O4/Fe3O4(001) structure","Takeshi Tainosho, Yanagihara Hideto, 介川 裕章","Takeshi Tainosho, Yanagihara Hideto, 介川 裕章","INTERMAG 2018","INTERMAG 2018","2018-04-23","","eng","oral_presentation","","","","","","Utilizing highly spin-polarized materials is a key to enlarge tunnel magnetoresistance (TMR) ratio of a magnetic tunnel junction (MTJ) and therefore, half metallic materials have been eagerly studied for decades. Among the various candidate substances of half metals, magnetite (Fe3O4) is attractive because of its high Curie temperature of ~850 K. Although much efforts had been paid for fabricating MTJs with Fe3O4 electrodes, the reported TMR ratios were not as high as ones expected for its half metallicity1. The origin of the significantly lower TMR of the MTJs with Fe3O4 electrodes is still controversial, but the characteristic film growth of Fe3O4(001), particularly generation of high-density anti-phase boundaries (APBs) in Fe3O4(001), could significantly reduce the local spin polarization at the interface. In order to solve the issue, building an all-spinel-type epitaxial MTJ by introducing a magnesium-aluminate MgAl2O4 tunnel barrier would be effective. Since ultra-thin Fe3O4(001) films on MgAl2O4(001) show the fewer anti-phase boundaries2, we can simply expect to improve the microstructure at Fe3O4(001) and MgAl2O4(001) interfaces. In this study, we developed the growth technique of a fully epitaxial Fe3O4/MgAl2O4/Fe3O4(001) structure by optimizing reactive sputtering method.","" "Large perpendicular magnetic anisotropy in Fe/MgAl2O4 heterostructures","Large perpendicular magnetic anisotropy in Fe/MgAl2O4 heterostructures","向 清懿, マンダル ルマ, 介川 裕章, 高橋 有紀子, 三谷 誠司","向 清懿, マンダル ルマ, 介川 裕章, 高橋 有紀子, 三谷 誠司"," 第79回応用物理学会秋季学術講演会"," 第79回応用物理学会秋季学術講演会","2018-09-18","","eng","oral_presentation","","","","","","MgAl2O4 is promising to substitute barrier material of MgO for magnetic tunnel junctions. By engineering the interface conditions through preparing MgAl2O4 barrier with direct electron beam evaporation method from a high density sintered target, a large PMA energy density is observed around ~1MJ/m3 after 400°C post-annealing. The PMA can survive after 500°C post-annealing and shows a weak measurement temperature dependence. The effective damping constant was also evaluated to be ~0.02 by time-resolved magneto-optic Kerr effect method under high magnetic fields. This study demonstrated robust interface PMA in ultrathin-Fe/MgAl2O4, which is useful for p-MTJ applications.","" "Large perpendicular magnetic anisotropy in Fe/MgAl2O4 heterostructures","Large perpendicular magnetic anisotropy in Fe/MgAl2O4 heterostructures","向 清懿, マンダル ルマ, 介川 裕章, 高橋 有紀子, 三谷 誠司","向 清懿, マンダル ルマ, 介川 裕章, 高橋 有紀子, 三谷 誠司","第42回日本磁気学会学術講演会","第42回日本磁気学会学術講演会","2018-09-11","","eng","oral_presentation","","","","","","MgAl2O4 is promising to substitute barrier material of MgO for magnetic tunnel junctions (MTJs) due to its tunable lattice constant. It is crucial to obtain large interfacial perpendicular magnetic anisotropy (PMA) at an MgAl2O4 for applications of perpendicularly magnetized MTJs (p-MTJs). A recent theoretical calculation indicates that an areal PMA energy density of ~1.3 mJ/m2 at an Fe/MgAl2O4(001) interface which is nearly comparable to that at an Fe/MgO(001) interface (~1.5-1.7 mJ/m2). However, a much smaller PMA energy density ~0.4 MJ/m3, comparing with ~1.4 MJ/m3 in Fe/MgO, has been experimentally reported in Fe/MgAl2O4(001) where the MgAl2O4 layers were prepared by post-oxidization of an Mg-Al alloy layer. Therefore, further improvement in the PMA energy of ultrathin-Fe/MgAl2O4(001) interfaces is expected if an optimized interface is obtained by suppressing atomic intermixing and over-oxidation through process optimization. In this study, we report the achievement of a large PMA at an Fe/MgAl2O4 by directly electron-beam deposition of MgAl2O4 instead of post-oxidation method.","" "Large perpendicular magnetic anisotropy in sputter-deposited Fe100-xAlx/MgAl2O4 heterostructures","Large perpendicular magnetic anisotropy in sputter-deposited Fe100-xAlx/MgAl2O4 heterostructures","シェーク トーマス, 介川 裕章, 徐 先東, 大久保 忠勝, 三谷 誠司, 宝野 和博","シェーク トーマス, 介川 裕章, 徐 先東, 大久保 忠勝, 三谷 誠司, 宝野 和博","第42回日本磁気学会学術講演会","第42回日本磁気学会学術講演会","2018-09-11","","eng","oral_presentation","","","","","","日本磁気学会においてFeAl合金超薄膜とスピネルバリアを組み合わせることで得られた大きな垂直磁気異方性について報告する。MgO基板/Cr/Fe80Al20(0.8 nm)/MgAl2O4構造において、450℃のアニール後に異方性エネルギーKeff = 1.1 MJ/m3と非常に高い垂直磁気異方性を示し、FeAl合金膜が垂直磁化MTJに有望であることがわかった。","" "多結晶CoFeB/MgAl2O4/CoFeB型強磁性トンネル接合における大きなトンネル磁気抵抗効果","多結晶CoFeB/MgAl2O4/CoFeB型強磁性トンネル接合における大きなトンネル磁気抵抗効果","イクティアル イクティアル, 介川 裕章, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","イクティアル イクティアル, 介川 裕章, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","第42回日本磁気学会学術講演会","第42回日本磁気学会学術講演会","2018-09-11","","jpn","oral_presentation","","","","","","","本発表ではCoFeB/MgAl2O4/CoFeB構造の多結晶MTJ構造の実現について日本磁気学会において発表する。極薄MgO層を下部CoFeBとMg-Al-O層界面に挿入することで(001)成長した均一バリアが実現され、室温で240%を超える高いTMR比と良好なバイアス電圧依存性が得られたことを報告する。" "Fe-Al/MgAl2O4/CoFeB perpendicular magnetic tunnel junctions with large perpendicular magnetic anisotropy","Fe-Al/MgAl2O4/CoFeB perpendicular magnetic tunnel junctions with large perpendicular magnetic anisotropy","シェーク トーマス, 介川 裕章, 徐 先東, 増田 啓介, 三浦 良雄, 三谷 誠司, 宝野 和博","シェーク トーマス, 介川 裕章, 徐 先東, 増田 啓介, 三浦 良雄, 三谷 誠司, 宝野 和博","9th Joint European Magnetic Symposia (JEMS2018)","9th Joint European Magnetic Symposia (JEMS2018)","2018-09-03","","eng","oral_presentation","","","","","","ドイツで行われるJEMS2018国際学会においてFeAl合金超薄膜とスピネルバリア界面における大きな垂直磁気異方性について、またFeAl/スピネル/CoFeB型の垂直磁化型MTJにおけるTMR効果について報告を行う。","" "Tunneling anisotropic magnetoresistance at high temperature in an Fe spin-dependent quantum well","Tunneling anisotropic magnetoresistance at high temperature in an Fe spin-dependent quantum well","アルマハドウイ ミフタ, 向 清懿, ベルムバーリク モハメド, 介川 裕章, 増田 啓介, 三浦 良雄, 三谷 誠司","アルマハドウイ ミフタ, 向 清懿, ベルムバーリク モハメド, 介川 裕章, 増田 啓介, 三浦 良雄, 三谷 誠司","9th Joint European Magnetic Symposia (JEMS2018)","9th Joint European Magnetic Symposia (JEMS2018)","2018-09-03","","eng","oral_presentation","","","","","","ドイツで行われるJEMS2018国際学会において、MgO sub./Cr/Fe超薄膜/MgAl2O4/CoFeB構造の90度磁化配置トンネル接合において、トンネル異方性磁気抵抗効果(TAMR)について報告する。Fe超薄膜層に形成した量子井戸準位によって大きなTAMR効果が得られ、室温以上でもTAMR効果が発現することなどを報告する。","" "Interface perpendicular magnetic anisotropy at a lattice-matched Co2FeAl/MgAl2O4 interface","Interface perpendicular magnetic anisotropy at a lattice-matched Co2FeAl/MgAl2O4 interface","介川 裕章, ハドーン ジェイソン ポール, 温 振超, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, ハドーン ジェイソン ポール, 温 振超, 大久保 忠勝, 三谷 誠司, 宝野 和博","9th Joint European Magnetic Symposia (JEMS2018)","9th Joint European Magnetic Symposia (JEMS2018)","2018-09-03","","eng","oral_presentation","","","","","","ドイツで行われるJEMS2018国際学会においてスピネルバリア(MgAl2O4)/Co2FeAl界面に誘起される垂直磁気異方性についての成果を発表する。酸化条件を最適化した構造において格子整合したエピタキシャル積層膜が実現するとともに、Al原子拡散によって強い磁気異方性が界面に現れ、垂直磁化膜が形成することを報告する。","" "Synthesis of spinel tunnel barriers for advanced spintronics devices ","Synthesis of spinel tunnel barriers for advanced spintronics devices ","介川 裕章","介川 裕章","The 21st International Conference on Magnetism (ICM2018)","The 21st International Conference on Magnetism (ICM2018)","2018-07-15","","eng","oral_presentation","","","","","","国際学会ICM2018においてスピネル系バリアの最新の研究進展についての招待講演を行う。","" "スピネルバリア強磁性トンネル接合の多結晶素子化 テクノロジーの確立","スピネルバリア強磁性トンネル接合の多結晶素子化 テクノロジーの確立","介川 裕章, イクティアル イクティアル, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","介川 裕章, イクティアル イクティアル, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","ImPACT佐橋プログラム公開成果報告会","ImPACT佐橋プログラム公開成果報告会","2018-06-29","","jpn","oral_presentation","","","","","","","本発表ではCoFeB/MgAl2O4/CoFeB構造の多結晶MTJ構造が実現されたことを報告する。バリア界面に薄いMgO層を結晶化テンプレート層として導入することでバリア層の(001)配向性の向上が実現され室温240%を超える高いTMR比と良好なバイアス電圧依存性が実現された。" "新規Fe 基合金Fe-Al超薄膜/スピネル界面における大きな垂直磁気異方性の観測とその電圧制御への取り組み","新規Fe 基合金Fe-Al超薄膜/スピネル界面における大きな垂直磁気異方性の観測とその電圧制御への取り組み","シェーク トーマス, アルマハドウイ ミフタ, 徐 先東, マンダル ルマ, 増田 啓介, 介川 裕章, 三浦 良雄, 高橋 有紀子, 大久保 忠勝, 三谷 誠司, 宝野 和博","シェーク トーマス, アルマハドウイ ミフタ, 徐 先東, マンダル ルマ, 増田 啓介, 介川 裕章, 三浦 良雄, 高橋 有紀子, 大久保 忠勝, 三谷 誠司, 宝野 和博","ImPACT佐橋プログラム公開成果報告会","ImPACT佐橋プログラム公開成果報告会","2018-06-29","","jpn","oral_presentation","","","","","","","磁性体を用いた情報不揮発性メモリであるMRAMは大容量化と動作電力の低減の実現が強く求められている状況にある。このため情報格納を担う強磁性トンネル接合(MTJ)素子のますますの微細化とより高効率な磁化反転技術の確立が必要とされている。微細化に伴う磁化情報の消失を避けるためには、記録層には非常に大きい垂直磁気異方性を付与させることが要求される。また、高効率な記録書き換えの有力な技術として電圧印加による磁気異方性変化(VCMA効果)を用いた磁化反転技術が盛んに研究されている。本研究では大きな垂直磁気異方性を示し、スパッタで作製可能な新規FeAl合金超薄膜/MgAl2O4積層構造を見いだしたことを報告する。また、FeAl超薄膜の垂直磁気異方性のVCMA効果を測定した結果も報告する。" "Low-temperature measurements of voltage-controlled magnetic anisotropy in Cr/Fe/MgAl2O4","Low-temperature measurements of voltage-controlled magnetic anisotropy in Cr/Fe/MgAl2O4","アルマハドウイ ミフタ, 向 清懿, ベルムバーリク モハメド, 介川 裕章, 葛西 伸哉, 三谷 誠司, 宝野 和博","アルマハドウイ ミフタ, 向 清懿, ベルムバーリク モハメド, 介川 裕章, 葛西 伸哉, 三谷 誠司, 宝野 和博","ImPACT佐橋プログラム公開成果報告会","ImPACT佐橋プログラム公開成果報告会","2018-06-29","","eng","oral_presentation","","","","","","MBEで作製された単結晶Cr/超薄Fe/MgAl2O4格子整合構造を持つ強磁性トンネル接合において、超薄Fe層内に形成された量子井戸準位が電圧-電流特性に明瞭に観測された。この量子井戸準位によって超薄Fe層の垂直磁気異方性の電圧変調定数VCMAやトンネル異方性磁気抵抗効果が増大する現象が観測された。","" "Highly (001)-textured MgAl2O4-based magnetic tunnel junctions with large magnetoresistance over 240%","Highly (001)-textured MgAl2O4-based magnetic tunnel junctions with large magnetoresistance over 240%","イクティアル イクティアル, 介川 裕章, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","イクティアル イクティアル, 介川 裕章, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","INTERMAG 2018","INTERMAG 2018","2018-04-23","","eng","oral_presentation","","","","","","本発表では、作製法の工夫によってCoFeB/MgAl2O4/CoFeB構造の多結晶MTJ構造が得られ、単結晶基板を用いずに高い特性を示す多結晶スピネル系MTJが実現されたことを報告する。極薄MgO層をCoFeB/スピネル界面に挿入することで、スピネル層の結晶化の促進と(001)配向性の向上が実現された。この結果として室温240%を超える高いTMR比と良好なバイアス電圧依存性が多結晶接合として実現された。","" "Atomic layer number dependence of voltage-controlled magnetic anisotropy in Cr/Fe/MgAl2O4 heterostructures","Atomic layer number dependence of voltage-controlled magnetic anisotropy in Cr/Fe/MgAl2O4 heterostructures","向 清懿, 介川 裕章, アルマハドウイ ミフタ, ベルムバーリク モハメド, 葛西 伸哉, 桜庭 裕弥, 三谷 誠司, 宝野 和博","向 清懿, 介川 裕章, アルマハドウイ ミフタ, ベルムバーリク モハメド, 葛西 伸哉, 桜庭 裕弥, 三谷 誠司, 宝野 和博","INTERMAG 2018","INTERMAG 2018","2018-04-23","","eng","oral_presentation","","","","","","MBEを用いて単結晶Cr/超薄膜Fe/MgAl2O4構造を実現し、その結果高い垂直磁気異方性が得られた。さらに、超薄膜Feの膜厚が偶数原子層厚の場合と奇数原子層厚の場合ではFe膜内に生じるスピン依存量子井戸の準位が大きく異なることから、界面垂直磁気異方性とそのVCMA効果に大きな変調がみられることが明らかになった。","" "Voltage control of perpendicular magnetic anisotropy in Fe/MgAl2O4 heterostructures","Voltage control of perpendicular magnetic anisotropy in Fe/MgAl2O4 heterostructures","向 清懿, 介川 裕章, アルマハドウイ ミフタ, ベルムバーリク モハメド, 葛西 伸哉, 桜庭 裕弥, 三谷 誠司, 宝野 和博","向 清懿, 介川 裕章, アルマハドウイ ミフタ, ベルムバーリク モハメド, 葛西 伸哉, 桜庭 裕弥, 三谷 誠司, 宝野 和博","第65回応用物理学会春季学術講演会","第65回応用物理学会春季学術講演会","2018-03-17","","eng","oral_presentation","","","","","","応用物理学会2017年秋季学術講演会における口頭発表が応用物理学会講演奨励賞の対象となったことから、本発表は受賞記念講演として行われる。MBEを用いて作製された単結晶Cr/超薄膜Fe/MgAl2O4界面には高い垂直磁気異方性が誘起される。興味深いことに、Fe膜厚が偶数原子層か奇数原子層かの違いによって垂直磁気異方性とそのVCMA効果に著しい違いがみられた。","" "Large interfacial perpendicular magnetic anisotropy in epitaxial Fe80Al20/MgAl2O4 heterostructures","Large interfacial perpendicular magnetic anisotropy in epitaxial Fe80Al20/MgAl2O4 heterostructures","シェーク トーマス, 介川 裕章, 徐 先東, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 徐 先東, 宝野 和博, 三谷 誠司","第65回応用物理学会春季学術講演会","第65回応用物理学会春季学術講演会","2018-03-17","","eng","oral_presentation","","","","","","Large perpendicular magnetic anisotropy (PMA) is a key requirement for future magnetic tunnel junction (MTJ) based devices. PMA at ferromagnet (FM)/oxide interfaces is used and extensively studied to compensate thermal instabilities arising with the downsizing of MTJs. Recently, strong PMA has been reported in Co2FeAl/MgAl2O4(001) heterostructures. Microstructure investigation revealed that the large PMA in the structure was attributed to a reduced lattice strain due to the use of MgAl2O4 and a strengthening of the effect of the Fe-O hybridization at the interfaces due to diffusion of Al into the barrier. In this study, we investigated the interfacial PMA using an Fe-Al alloy instead of Co2FeAl. We found enhanced effective PMA energy Keff up to 1.1 MJ/m3 in Fe80Al20 in contact with an MgAl2O4 barrier. ","" "CoFeB/MgAl2O4/CoFeB magnetic tunnel junctions with a large magnetoresistance over 240% at room temperature","CoFeB/MgAl2O4/CoFeB magnetic tunnel junctions with a large magnetoresistance over 240% at room temperature","イクティアル イクティアル, 介川 裕章, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","イクティアル イクティアル, 介川 裕章, 徐 先東, ベルムバーリク モハメド, リー ワチョル, 葛西 伸哉, 宝野 和博","第65回応用物理学会春季学術講演会","第65回応用物理学会春季学術講演会","2018-03-17","","eng","oral_presentation","","","","","","これまでスピネルバリアMTJは単結晶成長した場合のみ高いTMR比や良好なバイアス電圧依存性が報告されていた。本発表では、作製法を工夫することでCoFeB/MgAl2O4/CoFeB構造の多結晶MTJ構造が達成されたことを報告する。極薄MgO層をCoFeBとの界面に挿入することで(001)成長したスピネルバリアが実現されることを見いだし、これを用いて室温で240%を超える高いTMR比と良好なバイアス電圧依存性を達成した。","" "Epitaxial oxide barriers for magnetic tunnel junctions","Epitaxial oxide barriers for magnetic tunnel junctions","介川 裕章, 宝野 和博","介川 裕章, 宝野 和博","MP1308 TO-BE COST Action ""Towards Oxide-Based Electronics"" SPRING MEETING 2018","MP1308 TO-BE COST Action ""Towards Oxide-Based Electronics"" SPRING MEETING 2018","2018-03-12","","eng","oral_presentation","","","","","","EU内国際研究プログラムであるTO-BE COST Actionの""Towards Oxide-Based Electronics""プロジェクトのSPRING MEETING 2018において、単結晶酸化物を用いたスピントロニクス強磁性トンネル素子についてレビュー講演を行う。特に従来から使われているMgOトンネルバリアから、最新のスピネル系酸化物トンネルバリアについての現状と将来の展望について講演を行う。","" "Spinel for Coherent Tunneling Barriers in Magnetic Tunnel Junctions","Spinel for Coherent Tunneling Barriers in Magnetic Tunnel Junctions","シェーク トーマス, 介川 裕章, 三谷 誠司","シェーク トーマス, 介川 裕章, 三谷 誠司","Junjiro Kanamori Memorial International Symposium","Junjiro Kanamori Memorial International Symposium","2017-09-27","","jpn","oral_presentation","","","","","","","ピネルバリアを用いた強磁性トンネル接合に関する最近の研究成果を紹介する。Co2FeAl/MgAlO/Co2FeAl構造のMTJを用いた巨大TMR効果に加え、LiをドープしたMgAlOバリアMTJといった取り組みも述べる。" "New spintronic materials for magnetic tunnel junctions","New spintronic materials for magnetic tunnel junctions","介川 裕章, 向 清懿, 葛西 伸哉, アルマハドウイ ミフタ, ベルムバーリク モハメド, 向山 広記, イクティアル イクティアル, シェーク トーマス, チン カミン, 桜庭 裕弥, 大久保 忠勝, 増田 啓介, 三浦 良雄, 三谷 誠司, 宝野 和博","介川 裕章, 向 清懿, 葛西 伸哉, アルマハドウイ ミフタ, ベルムバーリク モハメド, 向山 広記, イクティアル イクティアル, シェーク トーマス, チン カミン, 桜庭 裕弥, 大久保 忠勝, 増田 啓介, 三浦 良雄, 三谷 誠司, 宝野 和博","The 3rd ImPACT International Symposium","The 3rd ImPACT International Symposium","2017-09-23","","jpn","oral_presentation","","","","","","","CoFeB/MgO/CoFeB perpendicular magnetic tunnel junctions (p-MTJs) are currently used in spin transfer torque magnetic random access memories (STT-MRAMs). In order to meet the ever-increasing demand for higher capacity MRAM, MTJs with higher TMR ratio larger than 300%, higher thermal stability (KV/kBT>60), and low-current switching are desired. In addition, the presence of grain boundaries in nanometer seized MTJ cells will become a critical issue for the reliability of high capacity MRAMs. To completely avoid the scattering of TMR behavior of nanosized MTJ cells, single crystalline devices epitaxially grown on Si ware may be desired. For better thermal stability, large PMA, either interfacial or bulk PMA, is required. For further reduction of the energy consumption for p-MTJ, usage of vo" "Control of epitaxial strain and magnetic anisotropy in cobalt-ferrite thin films by buffer layers","緩衝層膜によるコバルトフェライト薄膜の歪と磁気異方性制御","小野田 浩成, 井上 順一郎, 介川 裕章, Sonia Sharmin, 柳原 英人","小野田 浩成, 井上 順一郎, 介川 裕章, Sonia Sharmin, 柳原 英人","第41回日本磁気学会学術講演会","第41回日本磁気学会学術講演会","2017-09-19","","jpn","oral_presentation","","","","","","","MgO(001)上にエピタキシャル成膜されたコバルトフェライト(CoxFe3-xO4:CFO)膜は垂直磁気異方性を示し,その垂直磁気異方性エネルギーKuは14.7 Merg/cm3に達する.このCFO/MgO(001)膜における垂直磁気異方性は,基板との格子不整合(-0.48%)による磁気弾性効果で生じると理解されている.一方で,MgAl2O4(001)にCFO膜を成膜すると面内圧縮歪が導入され,Ku = -60 Merg/cm3が生じる.どちらの基板上に成膜した場合も,誘導されるKuは歪に対して線形に変化することが確認された .したがってこの格子歪の範囲では,CFOの誘起磁気異方性は現象論である磁気弾性効果によって定量的に説明できる.そのため,3~4%程度の引張り歪を導入することで,さらに大きな垂直磁気異方性の発現が期待できる.そこで本研究では,MgOと比して格子定数の大きいスピネル型酸化物Mg2SnO4(MSO)を緩衝層として導入し,その上に成膜したCFO膜の歪と磁気異方性の関係を実験的に明らかに" "MgGa2O4スピネルバリアを用いた低抵抗エピタキシャル強磁性トンネル接合","MgGa2O4スピネルバリアを用いた低抵抗エピタキシャル強磁性トンネル接合","介川 裕章, 加藤 侑志, ベルムバーリク モハメド, ポ ハン チェン, 大坊 忠臣, 下村 尚治, 上口 裕三, 伊藤 順一, 與田 博明, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, 加藤 侑志, ベルムバーリク モハメド, ポ ハン チェン, 大坊 忠臣, 下村 尚治, 上口 裕三, 伊藤 順一, 與田 博明, 大久保 忠勝, 三谷 誠司, 宝野 和博","第41回日本磁気学会学術講演会","第41回日本磁気学会学術講演会","2017-09-19","","jpn","oral_presentation","","","","","","","日本磁気学会において、新規スピネルバリア系MTJについて、特に低いバリア高さを持つ新スピネル材料MgGa2O4系MTJについて講演する。例えばFe/MgGa2O4/Fe構造において120%以上の室温TMR比を実現するとともに、既存MgOやMgAl2O4バリアよりも小さいバリア高さをもつことを実証したことを報告する。" "Perpendicular magnetic anisotropy at Fe/MgAl2O4 interfaces and its voltage effect","Perpendicular magnetic anisotropy at Fe/MgAl2O4 interfaces and its voltage effect","向 清懿, 介川 裕章, アルマハドウイ ミフタ, ベルムバーリク モハメド, 桜庭 裕弥, 葛西 伸哉, 宝野 和博, 三谷 誠司","向 清懿, 介川 裕章, アルマハドウイ ミフタ, ベルムバーリク モハメド, 桜庭 裕弥, 葛西 伸哉, 宝野 和博, 三谷 誠司","第41回日本磁気学会学術講演会","第41回日本磁気学会学術講演会","2017-09-19","","jpn","oral_presentation","","","","","","","電子線蒸着法で作製した超薄膜Fe/MgAl2O4(001)エピタキシャル界面における垂直磁気異方性(PMA)とその電圧変調(VCMA効果)について報告する。Fe層を1原子層(=約0.14 nm)の単位での精密な制御が実現され、高いPMAエネルギーも実現された。また、VCMA特性を評価したところ、PMAエネルギーがバイアス依存性に対して複雑に変化する挙動が明らかになった。さらにこの挙動は、Fe膜厚によっても大きく変化することもわかった。Cr下地とMgAl2O4バリア間のFe超薄膜内に形成された量子準位との関連が強く示唆される。" "Perpendicular magnetic anisotropy at lattice-matched Co2FeAl/MgAl2O4 interfaces","Co2FeAl/MgAl2O4格子整合界面における垂直磁気異方性","介川 裕章, ハドーン ジェイソン ポール, 温 振超, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, ハドーン ジェイソン ポール, 温 振超, 大久保 忠勝, 三谷 誠司, 宝野 和博","日本金属学会2017年秋期(第161回)講演大会","日本金属学会2017年秋期(第161回)講演大会","2017-09-06","","jpn","oral_presentation","","","","","","","超薄膜化したホイスラー合金Co2FeAl (CFA)層とMgAl2O4バリア界面における強い垂直磁気異方性(PMA)について報告する。CFAとMgAl2O4界面は格子整合しているため、格子不整合に起因する格子ひずみによる面内結晶磁気異方性を有効的に低減できる。これによって、従来のMgOバリアを用いた場合よりも強いPMAが達成されたことを報告する。" "Advanced magnetic tunnel junctions using spinel oxide barriers","Advanced magnetic tunnel junctions using spinel oxide barriers","介川 裕章","介川 裕章","The 28th Magnetic Recording Conference (TMRC 2017)","The 28th Magnetic Recording Conference (TMRC 2017)","2017-08-02","","jpn","oral_presentation","","","","","","","国際学会TMRC2017においてスピネル系バリアの研究進展についての招待講演を行う。" "スピントロニクス応用を支えるトンネル磁気抵抗素子用材料の開発","スピントロニクス応用を支えるトンネル磁気抵抗素子用材料の開発","介川 裕章","介川 裕章","先端材料異分野交流セミナー","先端材料異分野交流セミナー","2017-06-30","","jpn","oral_presentation","","","","","","","東北大学大学院工学研究科杉本諭教授主催の先端材料異分野交流セミナーにおいて、最新のスピントロニクス応用に関わるトンネル磁気抵抗素子(MTJ)について、特に材料の開発の観点から研究紹介を行った。MgAl2O4をはじめとする新規トンネルバリア材料やCo基ホイスラー合金を用いた素子などのトピックを中心に講演を行った。" "スピン依存トンネル伝導が関わるナノスピントロニクス素子の進展","スピン依存トンネル伝導が関わるナノスピントロニクス素子の進展","介川 裕章","介川 裕章","東京大学物性研究所 量子物質・ナノスケールセミナー","東京大学物性研究所 量子物質・ナノスケールセミナー","2017-05-25","","jpn","oral_presentation","","","","","","","TMR素子を中心に、スピン依存伝導が関わる磁気抵抗素子の歴史的経緯から最新の動向までを、特に材料の観点から概括をおこなう。また著者らがこれまでに関わってきたスピネル(MgAl2O4)系トンネルバリアや高スピン分極強磁性材料と知られるCo基ホイスラー合金の利用などについて紹介する。" "Origin of the increased damping of ultrathin films of Co2FeAl with perpendicular anisotropy","Origin of the increased damping of ultrathin films of Co2FeAl with perpendicular anisotropy","高橋 有紀子, 三浦 良雄, R. Choi, 大久保 忠勝, 温 振超, 石岡 邦江, マンダル ルマ, 介川 裕章, R Medapalli, 三谷 誠司, E.E. Fullerton, 宝野 和博","高橋 有紀子, 三浦 良雄, R. Choi, 大久保 忠勝, 温 振超, 石岡 邦江, マンダル ルマ, 介川 裕章, R Medapalli, 三谷 誠司, E.E. Fullerton, 宝野 和博","Intermag","Intermag","2017-04-24","","jpn","oral_presentation","","","","","","","We estimated the magnetic damping constant  of Co2FeAl (CFA) Heusler alloy films of different thicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect and ferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibited perpendicular magnetic anisotropy arising from the presence of the interface with MgO. While  increased gradually with decreasing CFA film thickness down to 1.2 nm, it was increased substantially when the thickness was reduced further to 1.0 nm. Based on the microstructure analyses and first-principal calculations, we attributed the origin of the large  in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereb" "Epitaxial magnetic tunnel junctions with a low barrier height spinel MgGa2O4","Epitaxial magnetic tunnel junctions with a low barrier height spinel MgGa2O4","介川 裕章, Yushi Kato, ベルムバーリク モハメド, ポ ハン チェン, Tadaomi Daibo, Naoharu Shimomura, Yuuzo Kamiguchi, Junichi Ito, Hiroaki Yoda, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, Yushi Kato, ベルムバーリク モハメド, ポ ハン チェン, Tadaomi Daibo, Naoharu Shimomura, Yuuzo Kamiguchi, Junichi Ito, Hiroaki Yoda, 大久保 忠勝, 三谷 誠司, 宝野 和博","INTERMAG Europe 2017","INTERMAG Europe 2017","2017-04-24","","jpn","oral_presentation","","","","","","","低いバリア高さを持つ新スピネル材料MgGa2O4をトンネル磁気抵抗素子(MTJ)のバリアとして開発した。Fe/MgGa2O4/Fe構造において室温で120%以上のトンネル磁気抵抗(TMR)比を実現するとともに、既存MgOやMgAl2O4バリアよりも小さいバリア高さをもつことを伝導特性の評価から実験的に実証した。本研究からスピネル系材料の新規開発によって、コヒーレントバリアの物性を実際に変調できることが明らかになり、今後TMRおよび界面磁気異方性特性の向上のために役立つ材料が提供できることが期待される。" "Tuning the magnetic properties and surface morphology of D022 Mn3-δGa film by N doping","Tuning the magnetic properties and surface morphology of D022 Mn3-δGa film by N doping","リー ワチョル, 介川 裕章, リュウ ジュン, 三谷 誠司, 宝野 和博","リー ワチョル, 介川 裕章, リュウ ジュン, 三谷 誠司, 宝野 和博","第64回応用物理学会春季学術講演会","第64回応用物理学会春季学術講演会","2017-03-14","","jpn","oral_presentation","","","","","","","In this work, we present tuning the magnetic properties and surface morphology of D022 Mn3-δGa using a small amount of N doping. 50 nm thick N-doped MnGa films were prepared by RF reactive sputtering technique on an MgO(001) single crystalline substrate at 480°C substrate temperature with the varied 0-0.66% N2 flow rate percentage (η) relative to Ar 30 sccm for two Mn3Ga and Mn2.5Ga compositions. N-doped Mn-Ga films all exhibited the gradual reduction in Ms up to 33-50% with the increasing N2 flow rate. In particular, N-doped Mn2.5Ga case revealed the single D022 structural phase formation with the high Ku ~ 1 MJ/m3 between η = 0-0.66% range despite the gradual reduction in magnetization, while N-doped Mn3Ga showed coherent growth of two D022 + E21 composite phases which results in the" "Magnetic tunnel junctions with a Li-substituted MgAl2O4 barrier","Magnetic tunnel junctions with a Li-substituted MgAl2O4 barrier","シェーク トーマス, 介川 裕章, 三谷 誠司","シェーク トーマス, 介川 裕章, 三谷 誠司","第64回応用物理学会春季学術講演会","第64回応用物理学会春季学術講演会","2017-03-14","","jpn","oral_presentation","","","","","","","Li-Mg-Al-Oの4元系スピネル酸化物をMTJ用バリアとする提案について、応物学会講演会において講演を行う。Fe/Li-Mg-Al-O/Feエピタキシャル成長MTJの作製に成功し、室温120%程度の比較的高いTMR比を実現した。このことはLiを含むバリア材質においてもコヒーレントトンネルによる高TMR比の達成が可能であること、また、4元系のスピネル酸化物がMTJ用バリアとして動作することを示しており、新スピネル系材質の可能性を広げる結果である。" "Development of a barrier material with a low barrier height for magnetic tunnel junctions: MgGa2O4 spinel oxide","低バリア高さを有する強磁性トンネル接合用バリア材料の開発:MgGa2O4スピネル酸化物","介川 裕章, 加藤 侑志, ベルムバーリク モハメド, ポ ハン チェン, 大坊 忠臣, 下村 尚治, 上口 裕三, 伊藤 順一, 與田 博明, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, 加藤 侑志, ベルムバーリク モハメド, ポ ハン チェン, 大坊 忠臣, 下村 尚治, 上口 裕三, 伊藤 順一, 與田 博明, 大久保 忠勝, 三谷 誠司, 宝野 和博","第64回応用物理学会春季学術講演会","第64回応用物理学会春季学術講演会","2017-03-14","","jpn","oral_presentation","","","","","","","低バリア高さを持つ新スピネル材料MgGa2O4をMTJのバリアとして開発したことを応物講演会において報告する。エピタキシャルFe/MgGa2O4/Fe構造がスパッタ法によって得られたこと、MgGa2O4がスピネル構造を有していること、コヒーレントトンネル効果が得られたことに加え、低抵抗化が実現可能であることが示された。将来の電圧駆動MRAMに向けた新規MTJバリ材料として期待される。" "Control of epitaxial strain and magnetic anisotropy in cobalt-ferrite thin film by buffer layers","緩衝層薄膜によるコバルトフェライト薄膜の歪と磁気異方性制御","小野田浩成, 久松裕季, 井上順一郎, 介川 裕章, 柳原英人","小野田浩成, 久松裕季, 井上順一郎, 介川 裕章, 柳原英人","第64回応用物理学会春季学術講演会","第64回応用物理学会春季学術講演会","2017-03-14","","jpn","oral_presentation","","","","","","","エピタキシャル成膜されたコバルトフェライト(CoxFe3−xO4:CFO)に3〜4%程度の引張り歪を導入することで,大きな垂直磁気異方性の発現が期待できる.本研究では,格子定数の大きいスピネル型酸化物を緩衝層として導入し,その上に成膜したCFO 薄膜の特性を調べ,歪と磁気異方性の関係を実験的に明らかにすることを試みた." "Giant tunnel magnetoresistance in epitaxially sputter-deposited spinel MgAl2O4(001) based magnetic tunnel junctions","スパッタ法により作製されたスピネルMgAl2O4(001)バリアを用いたエピタキシャル強磁性トンネル接合の巨大トンネル磁気抵抗効果","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","強的秩序とその操作に関わる研究グループ 第4回 研究会","強的秩序とその操作に関わる研究グループ 第4回 研究会","2017-01-04","","jpn","oral_presentation","","","","","","","In this talk, we will report a chemically homogenous MgAl2O4 tunnel barrier with a large tunnel magnetoresistance (TMR) ratio and a very flat Fe/MgAl2O4 barrier interfaces using direct sputtering from a sintered MgAl2O4 target. The typical magnetic tunnel junction (MTJ) structure is MgO(001) substrate/Cr (40)/Fe (100)/Mg-Al/MgAl2O4/Fe (7)/IrMn (12)/Ru (10), units in nm. A large TMR ratio of 245% at room temperature was observed, which exceeded that of epitaxial Fe/post-oxidized MgAl2O4/Fe (~212%) MTJs. These results indicate that the direct sputtering of MgAl2O4 is an alternative way for achieving high performance spinel barrier-based MTJs." "Voltage control of magnetic anisotropy in monocrystalline ferromagnetic metal/oxide layered structures","Voltage control of magnetic anisotropy in monocrystalline ferromagnetic metal/oxide layered structures","三谷 誠司, 温 振超, 向 清懿, 飯田 裕希, 介川 裕章, 葛西 伸哉","三谷 誠司, 温 振超, 向 清懿, 飯田 裕希, 介川 裕章, 葛西 伸哉","Korean Magnetics Society Meeting","Korean Magnetics Society Meeting","2016-11-23","","jpn","oral_presentation","","","","","","","磁性体ナノ構造における界面垂直磁気異方性とその電圧効果に関して、物材機構・磁性スピントロニクス材料研究拠点での研究成果のレビューを行う。特に磁気異方性に及ぼす電圧効果について、関連データとの比較も含めて詳しく発表する。" "Spintronics application of spinel-based tunnel barriers","スピネル系トンネルバリアのスピントロニクス素子応用","介川裕章","介川裕章","応用電子物性分科会・スピントロニクス研究会 共催研究会","応用電子物性分科会・スピントロニクス研究会 共催研究会","2016-11-22","","jpn","oral_presentation","","","","","","","応用物理学会の応用電子物性分科会・スピントロニクス研究会の共催研究会において招待講演を行う。スピネル系バリアを用いたスピントロニクス素子展開に主眼を置き、スピネルバリア研究の最近の進展について幅広く講演を行う。例えばスピネル焼結ターゲットからの直接スパッタによるバリア作製法や電圧MRAMを見据えた低抵抗MTJや界面誘起垂直磁化構造などについての報告を行う。" "Epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions prepared by a direct sputtering technique and Mg-Al insertion","Epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions prepared by a direct sputtering technique and Mg-Al insertion","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","61st Annual Conference on Magnetism and Magnetic Materials (MMM)","61st Annual Conference on Magnetism and Magnetic Materials (MMM)","2016-10-31","","jpn","oral_presentation","","","","","","","直接スパッタ法を用いてMgAl2O4バリアを作製することに成功し、Fe/MgAl2O4/Fe構造において極めて高品質なエピタキシャル成長の実現と大きな室温TMR比が達成されたことを国際学会MMMにおいて報告する。本公演ではMgAl金属層をFe/バリア界面に薄く挿入する効果を確認し、非常に薄い0.1 nm以下のMgAl挿入が高いTMR比を得るために有効であることを見いだしたことも併せて報告する。" "Cation-ordered MgAl2O4 magnetic tunnel junctions with highly spin-polarized Co2FeAl electrodes","Cation-ordered MgAl2O4 magnetic tunnel junctions with highly spin-polarized Co2FeAl electrodes","シェーク トーマス, 介川 裕章, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","61st Annual Conference on Magnetism and Magnetic Materials (MMM)","61st Annual Conference on Magnetism and Magnetic Materials (MMM)","2016-10-31","","jpn","oral_presentation","","","","","","","国際学会MMMにおいて高スピン分極材料であるCo2FeAlを用いたCo2FeAl/MgAl2O4/Co2FeAl構造を持つ強磁性トンネル接合について報告する。本研究ではMgAl2O4スピネルバリアの上下電極として高品質なCo2FeAl達成したことで規則化したスピネルをバリアとして用いた場合においても高いTMR比が実現可能であることを示した。" "Interfacial perpendicular magnetization and atomic interdiffusion at Co2FeAl/MgAl2O4 spinel interface","Interfacial perpendicular magnetization and atomic interdiffusion at Co2FeAl/MgAl2O4 spinel interface","介川 裕章, ハドーン ジェイソン ポール, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, ハドーン ジェイソン ポール, 大久保 忠勝, 三谷 誠司, 宝野 和博","61st Annual Conference on Magnetism and Magnetic Materials (MMM)","61st Annual Conference on Magnetism and Magnetic Materials (MMM)","2016-10-31","","jpn","oral_presentation","","","","","","","スピネルバリア(MgAl2O4)/Co2FeAl超薄膜構造を作製し、その界面に誘起される垂直磁気異方性についての成果を国際学会MMMにて講演をおこなう。酸化条件を最適化した構造において格子整合したエピタキシャル積層膜が実現するとともに、強い磁気異方性が界面に現れ、垂直磁化膜が形成することを報告する。" "Lattice-matched Co2FeAl/cation-ordered MgAl2O4/Co2FeAl Magnetic Tunnel Junctions with Large Tunnel Magnetoresistance exceeding 300%","Lattice-matched Co2FeAl/cation-ordered MgAl2O4/Co2FeAl Magnetic Tunnel Junctions with Large Tunnel Magnetoresistance exceeding 300%","シェーク トーマス, 介川 裕章, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","2nd ImPACT International Symposium on Spintronic Memory, Circu","2nd ImPACT International Symposium on Spintronic Memory, Circu","2016-09-30","","jpn","oral_presentation","","","","","","","本研究ではスピネルバリアの上下に高スピン分極材料(Co2FeAl)を高品質に作製することで規則化したスピネルバリアを用いて高いTMR比が実現可能であることを示した。これまでスピネル規則構造を持つMTJでは高いTMR比が得られていなかったが、作製条件の検討によって室温TMR比は最大340%と非常に大きくなり、スピネルバリアMTJのTMR比のなかで一番大きな値が得られたことを報告する。" "Giant tunnel magnetoresistance in epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions prepared by a direct sputtering technique","Giant tunnel magnetoresistance in epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions prepared by a direct sputtering technique","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","2nd ImPACT International Symposium on Spintronic Memory, Circu","2nd ImPACT International Symposium on Spintronic Memory, Circu","2016-09-30","","jpn","oral_presentation","","","","","","","スパッタを用いて単結晶MgAl2O4バリアを作成する技術を開発し、それを用いて作製したFe/MgAl2O4/Fe構造において高品質なエピタキシャル成長の実現と245%の大きな室温TMR比を達成したことについて報告する。" "Effect of an Mg-Al insertion on the directly sputtered epitaxial MgAl2O4(001)-based magnetic tunnel junctions","Effect of an Mg-Al insertion on the directly sputtered epitaxial MgAl2O4(001)-based magnetic tunnel junctions","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","SSDM2016","SSDM2016","2016-09-26","","jpn","oral_presentation","","","","","","","スパッタで作製したMgAl2O4バリアを用いて作製したFe/MgAl2O4/Fe構造において極めて高品質なエピタキシャル成長の実現と245%の大きな室温TMR比の達成を報告する。また、MgAl金属層をFe/バリア界面に薄く挿入する効果を確認し、非常に薄い0.1 nm以下のMgAl挿入が高いTMR比を得るために有効であることを見いだした。" "Realization of high quality epitaxial current-perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001) wafer using NiAl buffer layer","Realization of high quality epitaxial current-perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001) wafer using NiAl buffer layer","チン カミン, リュウ ジュン, 桜庭 裕弥, 介川 裕章, リ ソンテン, 宝野 和博","チン カミン, リュウ ジュン, 桜庭 裕弥, 介川 裕章, リ ソンテン, 宝野 和博","The 77th JSAP Autumn Meeting","The 77th JSAP Autumn Meeting","2016-09-13","","jpn","oral_presentation","","","","","","","In this letter, we reported NiAl buffer layer as a template for the integration of epitaxial CPP-GMR devices on a Si(001) single crystalline substrate. By depositing NiAl on Si at an elevated temperature of 500 degrees centigrade, a smooth and epitaxial B2-type NiAl(001) layer was obtained. The surface roughness was further improved by depositing Ag on the NiAl layer and applying subsequent annealing process. The epitaxial CPP-GMR devices grown on the buffered Si(001) substrate present a comparable large MR output with the devices grown on an MgO(001) substrate, demonstrating the possibility of epitaxial spintronic devices with NiAl template for practical applications. " "High quality cation-disorder MgAl2O4(001)-based magnetic tunnel junctions deposited by a direct sputtering technique","High quality cation-disorder MgAl2O4(001)-based magnetic tunnel junctions deposited by a direct sputtering technique","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","第40回日本磁気学会学術講演会","第40回日本磁気学会学術講演会","2016-09-05","","jpn","oral_presentation","","","","","","","日本磁気学会学術講演会(金沢)において、MgAl2O4をトンネルバリアとする強磁性トンネル接合について報告する。主にスピネルターゲットからの直接スパッタ法を採用することによって、きわめて平坦なコヒーレントバリアが形成できること、これによって電圧MRAMを見据えた低抵抗MTJや界面誘起垂直磁化構造の作製のための知見が得られたことを報告する。" "Realization of high quality epitaxial current-perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001) wafer ","Realization of high quality epitaxial current-perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001) wafer ","CHEN, Jiamin, LIU, Jun, SAKURABA, Yuya, SUKEGAWA, Hiroaki, LI, Songtian, HONO, Kazuhiro","CHEN, Jiamin, LIU, Jun, SAKURABA, Yuya, SUKEGAWA, Hiroaki, LI, Songtian, HONO, Kazuhiro","The 40th Annual Conference on Magnetics in Japan","The 40th Annual Conference on Magnetics in Japan","2016-09-05","","eng","oral_presentation","","","","","","In this letter, we reported NiAl buffer layer as a template for the integration of epitaxial CPP-GMR devices on a Si(001) single crystalline substrate. By depositing NiAl on Si at an elevated temperature of 500C, a smooth and epitaxial B2-type NiAl(001) layer was obtained. The surface roughness was further improved by depositing Ag on the NiAl layer and applying subsequent annealing process. The epitaxial CPP-GMR devices grown on the buffered Si(001) substrate present a comparable large MR output with the devices grown on an MgO(001) substrate, demonstrating the possibility of epitaxial spintronic devices with NiAl template for practical applications.","" "MgAl2O4 spinel based magnetic tunnel junctions and related topics","MgAl2O4 spinel based magnetic tunnel junctions and related topics","介川 裕章","介川 裕章","8th Joint European Magnetic Symposia (JEMS2016)","8th Joint European Magnetic Symposia (JEMS2016)","2016-08-21","","jpn","oral_presentation","","","","","","","英国グラスゴーで開催される磁性に関する国際学会JEMS2016において、MgAl2O4をトンネルバリアとする強磁性トンネル接合、強磁性との界面に誘起される垂直磁気異方性、新スピネルバリア材料など、幅広いスピネルバリア研究と関連現象について30分の招待講演を行う。" "Recent progress in MgAl2O4-based magnetic tunnel junctions with a tunable lattice spacing","Recent progress in MgAl2O4-based magnetic tunnel junctions with a tunable lattice spacing","介川 裕章, ベルムバーリク モハメド, シェーク トーマス, 三谷 誠司","介川 裕章, ベルムバーリク モハメド, シェーク トーマス, 三谷 誠司","3rd Workshop of the Core-to-Core Project Tohoku-York-Kaiserslaut","3rd Workshop of the Core-to-Core Project Tohoku-York-Kaiserslaut","2016-06-22","","jpn","oral_presentation","","","","","","","国際会議において強磁性トンネル接合用MgAl2O4トンネルバリアについての最新研究と動向について招待講演する。特に、新しい作製方法である直接スパッタ法による高品質MgAl2O4バリア作製について、さらにCo2FeAlホイスラー合金を用いたトンネル磁気抵抗の高出力化について講演を行う。" "Development of new materials for magnetic tunnel junctions - lattice-matched spinel barrier and highly spin-polarized Heusler alloys -","強磁性トンネル接合用新規材料開発 -格子整合スピネルバリアと高スピン分極ホイスラー合金-","介川 裕章, 三谷 誠司","介川 裕章, 三谷 誠司","日本磁気学会第208回研究会/第56回化合物新磁性材料専門研究会","日本磁気学会第208回研究会/第56回化合物新磁性材料専門研究会","2016-06-09","","jpn","oral_presentation","","","","","","","日本磁気学会主催の第208回研究会/第56回化合物新磁性材料専門研究会「スピントロニクスにおける次世代材料開発」に出席し、招待講演を行う。本講演では強磁性トンネル素子のトンネルバリア層用の新材料であるスピネルMgAl2O4についての最新の研究と展望を述べる。特に、最近確立した直接スパッタ法によるMgAl2O4超薄膜の作製や、高スピン分極率を有するCo基ホイスラー合金であるCo2FeAl層を組み合わせた特性の向上について詳しく講演を行う。" "Large tunnel magnetoresistance in Co2FeAl/MgAl2O4/Co2FeAl junctions free from the band folding effect","Large tunnel magnetoresistance in Co2FeAl/MgAl2O4/Co2FeAl junctions free from the band folding effect","シェーク トーマス, 介川 裕章, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","第63回応用物理学会春季学術講演会","第63回応用物理学会春季学術講演会","2016-03-19","","jpn","oral_presentation","","","","","","","これまでスピネルバリアMTJにおいて高いTMR比を得るためにはスピネル構造規則化を防ぐ必要があった。本研究では上下に高スピン分極材料(Co2FeAl)を高品質に作製することで規則化したスピネルバリアを用いても高いTMR比が実現可能であることを示した。適切なアニールを行うことで室温TMR比は最大340%をこえ、スピネルバリアMTJのTMR比のなかで一番大きな値が得られた。" "Giant tunnel magnetoresistance using a cation-disorder MgAl2O4 (001) epitaxial barrier deposited by direct sputtering technique","Giant tunnel magnetoresistance using a cation-disorder MgAl2O4 (001) epitaxial barrier deposited by direct sputtering technique","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","ベルムバーリク モハメド, 介川 裕章, 大久保 忠勝, 三谷 誠司, 宝野 和博","第63回応用物理学会春季学術講演会","第63回応用物理学会春季学術講演会","2016-03-19","","jpn","oral_presentation","","","","","","","これまでスピネルバリアMTJのバリア層作製にはMg-Al合金の後酸化処理を専ら用いられてきた。しかし平坦化が困難という問題があった。本講演ではスピネル酸化物ターゲットからの直接スパッタを新たに用い後酸化法よりも高品質なスピネルバリアを作製でき、TMR比向上が可能であるという実用上も重要な結果が得られたことを報告する。" "Current status and prospect of a spinel tunnel barrier for spintronic magnetoresistive devices","スピントロニクス磁気抵抗素子用スピネル系トンネルバリアの現状と展望","介川 裕章, ベルムバーリク モハメド, シェーク トーマス, 三谷 誠司","介川 裕章, ベルムバーリク モハメド, シェーク トーマス, 三谷 誠司","強的秩序とその操作に関する第一回研究会","強的秩序とその操作に関する第一回研究会","2016-01-04","","jpn","oral_presentation","","","","","","","本講演では、主にスピネルバリアMTJ 用トンネルバリアの我々の取り組みとその展望について紹介する。単結晶成長を用いたスピネルバリアの高品質化による大きなTMR比の実現やバイアス電圧特性の向上などについて述べる。また、スピネルバリア研究の過程において明らかになったスピン依存伝導現象についての知見についても紹介する。例えば、スピネルのように大きな格子ユニットをもつバリア材料を用いた時に起こる「バンド折りたたみ」とよばれる効果によってTMR 比の著しい低下が起こるという問題とその解決法について触れる。" "Interface perpendicular magnetic anisotropy in ferromagnetic metal/oxide heterostructures and magnetic tunnel junctions","Interface perpendicular magnetic anisotropy in ferromagnetic metal/oxide heterostructures and magnetic tunnel junctions","三谷 誠司, 向 清懿, 具 正祐, 温 振超, 介川 裕章","三谷 誠司, 向 清懿, 具 正祐, 温 振超, 介川 裕章","14th IUMRS-ICAM","14th IUMRS-ICAM","2015-10-25","","jpn","oral_presentation","","","","","","","強磁性金属/酸化物界面および強磁性トンネル接合の垂直磁気異方性に関して、最近の応用開発を踏まえてNIMSの研究成果を中心にレビューする。Fe系合金における巨大な垂直磁気異方性の実現や、新規酸化物および新規メカニズムに関する最近の取り組みを紹介する。" "Perpendicular magnetization epitaxial films using Heusler-derived materials","Perpendicular magnetization epitaxial films using Heusler-derived materials","介川 裕章","介川 裕章","4th Japan-EU Oepn Workshop on "HARFIR"","4th Japan-EU Oepn Workshop on "HARFIR"","2015-10-06","","jpn","oral_presentation","","","","","","","In this talk, I will show recent works on Co2FeAl (CFA)-based spintronic heterostructures. Firstly, I will introduce a perpendicularly magnetized ultrathin CFA film using an MgO interface. We found that the strong perpendicular magnetic anisotropy (PMA) was induced at an ultrathin CFA/MgO interface. Secondly, I will talk about CFA-based MTJs in combination with a newly-developed spinel MgAl2O4 epitaxial barrier." "Current stage and prospect of a spinel barrier for magnetic tunnel junctions","強磁性トンネル素子用スピネルバリア研究の現状と展望","介川 裕章","介川 裕章","IDEMAヘッド・ディスク部会ワークショップ","IDEMAヘッド・ディスク部会ワークショップ","2015-10-02","","jpn","oral_presentation","","","","","","","これまで研究開発を進めてきたスピントロニクスデバイス用トンネルバリア材料、スピネルバリアについての最近状況と展望を講演する。" "Magnetic tunnel junctions and perpendicular magnetization films using Heusler alloy Co2FeAl","ホイスラー合金Co2FeAl薄膜を用いた強磁性トンネル接合と垂直磁化膜","介川 裕章, 温 振超, シェーク トーマス, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","介川 裕章, 温 振超, シェーク トーマス, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","日本金属学会2015年秋期講演大会","日本金属学会2015年秋期講演大会","2015-09-16","","jpn","oral_presentation","","","","","","","Co基ホイスラー合金は、高いスピン分極率、低い磁気ダンピング、高いキュリー温度を持つことから磁気ランダムアクセスメモリー等への応用が期待される強磁性材料系である。ホイスラー合金を強磁性トンネル素子(MTJ)に用いる場合MgO等のトンネルバリアと組み合わせることが必要であるため、高品質な界面構造を作製可能で、高いトンネル磁気抵抗比(TMR比)が得られる材料組成であることが求められる。また、微小素子においても十分高い熱安定性が確保でき、同時に高効率なスピントルク(STT)磁化反転書込みのためには、垂直磁化膜であることも求められる。我々は、ホイスラー合金として、MgOバリアと格子整合性が良く、コヒーレントトンネル効果が期待できるCo2FeAl (CFA)に注目してきた。本講演では、CFAを用いたMTJ構造における高いTMR比の実現、STT磁化反転動作の実証に加え、極薄CFA/MgO積層構造における界面誘起垂直磁化CFA膜について報告する。また、最" "Fabrication of perpendicular magnetization films using an ultrathin Co2FeAl/MgAl2O4 epitaxial stack","超薄Co2FeAl/MgAl2O4エピタキシャル積層構造を用いた垂直磁化膜の作製","介川 裕章, ハドーン ジェイソン ポール, 大久保 忠勝, 宝野 和博, 三谷 誠司","介川 裕章, ハドーン ジェイソン ポール, 大久保 忠勝, 宝野 和博, 三谷 誠司","第39回日本磁気学会学術講演会","第39回日本磁気学会学術講演会","2015-09-08","","jpn","oral_presentation","","","","","","","酸化物層と強磁性層との界面に誘起される強い垂直磁気異方性を利用した垂直磁化膜構造が近年大きな注目を集めている。特にスピン注入書込型磁気ランダムアクセスメモリ(STT-MRAM)への応用にむけて、高いトンネル磁気抵抗(TMR)比が得られるMgOバリアとCoFeBを組み合わせた構造が盛んに研究されている。また、強磁性体層としてFe やCo2FeAl(CFA)合金を用いることによってもMgOとの界面に大きな垂直磁気異方性が誘起されることが報告されている。一方、これらの強磁性体とMgOとの間には3~4%程度の格子不整合が存在するため、これらの界面においてミスフィット転位や格子ひずみの導入によって構造が乱されうるという問題がある。MgAl2O4をベースとするバリアはより理想的な界面構造の作製が期待でき垂直磁気異方性をさらに向上できる可能性を秘めている。本研究ではエピタキシャルCFA超薄膜とMgAl2O4薄膜を積層させることにより大きな垂直磁気異方性が得られ" "Interface-induced perpendicular magnetic anisotropy and giant tunnel magnetoresistance in Co2FeAl Heusler alloy based heterostructures","Interface-induced perpendicular magnetic anisotropy and giant tunnel magnetoresistance in Co2FeAl Heusler alloy based heterostructures","介川 裕章","介川 裕章","Heusler Alloys for Spintronic Devices","Heusler Alloys for Spintronic Devices","2015-07-30","","jpn","oral_presentation","","","","","","","In this talk, I will show recent works on Co2FeAl (CFA)-based spintronic heterostructures. Firstly, I will introduce a perpendicularly magnetized ultrathin CFA film using an MgO interface. We found that the strong perpendicular magnetic anisotropy (PMA) was induced at an ultrathin CFA (~ 1 nm)/MgO interface. Interestingly, large PMA energy is observed when a Ru buffer layer with a (02-23) high-index orientation is used. Secondly, I will talk about CFA-based MTJs in combination with a newly-developed spinel MgAl2O4 epitaxial barrier. MgAl2O4-based MTJs exhibit giant TMR effect due to the coherent tunneling like MgO-based MTJs. Importantly, the lattice spacing of the MgAl2O4 can be easily tuned by Mg-Al composition of the layer, which enables us to achieve a lattice-matched MgAl2O4/bcc-based" "Development of epitaxial CPP-GMR devices with half-metallic Heusler electrode","高MRホイスラー合金電極エピタキシャル巨大磁気抵抗素子の作製","桜庭 裕弥, チン カミン, チョン ジン ウォン, 古林 孝夫, 宝野 和博, 介川 裕章","桜庭 裕弥, チン カミン, チョン ジン ウォン, 古林 孝夫, 宝野 和博, 介川 裕章","ImPACT Program プロジェクト3 単結晶化・高集積化・3次元化プロジェ","ImPACT Program プロジェクト3 単結晶化・高集積化・3次元化プロジェ","2015-07-23","","jpn","oral_presentation","","","","","","","ImPACT単結晶化プロジェクトに関する成果報告を行う。NiAl挿入層を用いたCPP-GMR素子における70%を超える磁気抵抗比の他、Si基板上にNiAl下地層を用いた素子において良好な素子が作製できたことについて言及する。" "Perpendicularly magnetized MnGa polycrystalline film growth on (001)-textured (Mg0.2Ti0.8)O buffer with SiO2/Si substrate","Perpendicularly magnetized MnGa polycrystalline film growth on (001)-textured (Mg0.2Ti0.8)O buffer with SiO2/Si substrate","リー ワチョル, 介川 裕章, リュウ ジュン, 大久保 忠勝, 三谷 誠司, 宝野 和博","リー ワチョル, 介川 裕章, リュウ ジュン, 大久保 忠勝, 三谷 誠司, 宝野 和博","22nd International Colloquium on Magnetic Films and Surfaces","22nd International Colloquium on Magnetic Films and Surfaces","2015-07-12","","jpn","oral_presentation","","","","","","","Recently, tetragonal MnGa alloys have attracted great interest as a candidate ferromagnetic material for future spin-transfer torque magnetoresistive random access memory. The ordered MnGa film growth has been reported only with the use of a single crystal substrate, and highly-textured buffer layer such as Cr, or Pt, so far. In the literature, the lattice spacing, magnetic properties and the optimum growth condition of MnGa film are all known to be strongly dependent on the seeding layer[3], which causes difficulties in achieving the textured MnGa film without a single crystal substrate. In this work, we report the successful growth of (100)-textured polycrystalline D022 Mn2.4Ga film with PMA on an amorphous SiO2/Si substrate using a conductive oxide (Mg0.2Ti0.8)O buffer layer. " "Temperature dependence of lattice-matched Co2FeAl/Mg-Al-O/CoFe magnetic tunnel junctions","Temperature dependence of lattice-matched Co2FeAl/Mg-Al-O/CoFe magnetic tunnel junctions","シェーク トーマス, 介川 裕章, 古林 孝夫, 温 振超, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","シェーク トーマス, 介川 裕章, 古林 孝夫, 温 振超, 猪俣 浩一郎, 大久保 忠勝, 宝野 和博, 三谷 誠司","22nd International Colloquium on Magnetic Films and Surfaces","22nd International Colloquium on Magnetic Films and Surfaces","2015-07-12","","jpn","oral_presentation","","","","","","","On the road to high TMR junctions, we recently have shown a giant TMR ratio in perfectly lattice-matched Co2FeAl (CFA)/cation-disordered Mg-Al-O/CoFe junctions (~230% TMR at RT) confirmed by transmission electron microscopy (TEM) analyses. Besides the good lattice-matching, inserting up to 1 nm CoFe between the Heusler electrode and spinel barrier results in strongly enhanced TMR ratios up to ~280%. We attributed this enhancement to the reduction of oxidation or intermixing at the interface; this indicates importance of controlling barrier interface states in addition to the lattice-spacing matching. In this study, we focus on the temperature dependence of TMR ratios and relate it to the microstructure of CFA/CoFe (dCoFe)/Mg-Al-O/ CoFe junctions. " "Bias voltage dependence of tunnel magnetoresistance in spinel Mg-Al-O based epitaxial tunnel junctions","Bias voltage dependence of tunnel magnetoresistance in spinel Mg-Al-O based epitaxial tunnel junctions","介川 裕章, 猪俣 浩一郎, 三谷 誠司","介川 裕章, 猪俣 浩一郎, 三谷 誠司","22nd International Colloquium on Magnetic Films and Surfaces","22nd International Colloquium on Magnetic Films and Surfaces","2015-07-12","","jpn","oral_presentation","","","","","","","A magnetic tunnel junction (MTJ) is one of the most important magnetoresistive devices in spintronics. MTJs are used for a read sensor in hard disc drives and memory cells of magnetoresistive random access memories. To develop high performance devices, improving an output voltage of an MTJ, i.e., improving a tunnel magnetoresistance (TMR) ratio and suppressing bias voltage dependence of TMR, is strongly required. However, the mechanism of the bias voltage dependence of TMR is not well understood. The bias voltage dependence of TMR may also be affected by the barrier interface electronic state and crystallinity of the barrier. In this study, using lattice-matched MgAl2O4 barrier, we investigated how the bias voltage dependence of TMR properties of an Fe/Mg-Al-O/Fe MTJ changes with the oxida" "Development of epitaxial CPP-GMR devices with half-metallic Heusler electrode on Si-substrate","Si基板上へのホイスラー合金ハーフメタルを用いた単結晶CPP-GMR素子の作製","桜庭 裕弥, チン カミン, 古林 孝夫, 介川 裕章, 宝野 和博","桜庭 裕弥, チン カミン, 古林 孝夫, 介川 裕章, 宝野 和博","ImPACT国際シンポジウム","ImPACT国際シンポジウム","2015-06-21","","jpn","oral_presentation","","","","","","","JST ImPACT 佐橋PMプロジェクト 国際シンポジウムにおいて講演を行う。単結晶・3次元化プロジェクトのテーマと関連しSi基板上に作製したエピタキシャルCPP-GMR素子に関する研究報告を行う。" "Toward low resistive epitaxial magnetic tunnel junctions using a spinel-based barrier","Toward low resistive epitaxial magnetic tunnel junctions using a spinel-based barrier","介川 裕章, シェーク トーマス, 大久保 忠勝, 三谷 誠司, 宝野 和博","介川 裕章, シェーク トーマス, 大久保 忠勝, 三谷 誠司, 宝野 和博","The 1st ImPACT International Symposium on Spintronic Memory,","The 1st ImPACT International Symposium on Spintronic Memory,","2015-06-21","","jpn","oral_presentation","","","","","","","ImPACTプロジェクト国際シンポジウムにおいて、低抵抗バリア実現に向けて行っている新バリア材料:スピネルMgAl2O4を用いた単結晶強磁性トンネル接合についてのNIMSの研究取り組みについてポスター講演を行う。" "Bias voltage dependence in magnetic tunnel junctions with a spinel Mg-Al-O barrier","スピネルMg-Al-Oバリアを有する強磁性トンネル接合のバイアス電圧依存性","介川 裕章, 猪俣 浩一郎, 三谷 誠司","介川 裕章, 猪俣 浩一郎, 三谷 誠司","第62回応用物理学会春季学術講演会","第62回応用物理学会春季学術講演会","2015-03-11","","jpn","oral_presentation","","","","","","","スピネル(MgAl2O4)は強磁性トンネル接合(MTJ)用のバリアとして適した材料の一つであり、スピネル構造を不規則化させたCation-disorderスピネル構造(Mg-Al-O)を実現することで室温300%を超える高いトンネル磁気抵抗(TMR)比が得られるため、磁気ランダムアクセスメモリや高性能磁気センサーなどへの応用が期待される。スピネルバリアの大きな利点はCoFe合金やホイスラー合金等と(001)方位でほぼ完全に格子整合させることが可能であることである。このことはバイアス電圧印加下によるTMR比の減衰の抑制につながり、Fe電極を用いた場合TMR比が半減するバイアス電圧は室温で優に1 Vを超える値を示す。そのため、応用上重要な有限バイアス下における電圧出力を大きく向上できる。したがって、スピネルバリアMTJのバイアス特性を詳細に明らかにすることは素子特性向上のために重要である。本研究ではMg-Al-OバリアMTJのバイアス依存性や微分コンダクタンス特性" "Perfectly lattice-matched magnetic tunnel junctions using a spinel MgAl2O4-based barrier","MgAl2O4スピネル系バリアを用いた 完全格子整合強磁性トンネル接合","介川 裕章","介川 裕章","第169回スピニクス研究会","第169回スピニクス研究会","2014-12-12","","jpn","oral_presentation","","","","","","","東北大学電気通信研究所、工学研究会、第169回スピニクス研究会『最先端スピントロニクスと酸化物薄膜』の招待講演として、MgAl2O4スピネル系バリアを用いた完全格子整合強磁性トンネル接合についての最新研究内容を講演する。 " "Exchange interaction in Co/Tb/Co trilayer structures","Exchange interaction in Co/Tb/Co trilayer structures","Q.Y. Xiang, 温 振超, 介川 裕章, 三谷 誠司","Q.Y. Xiang, 温 振超, 介川 裕章, 三谷 誠司","応用物理学会秋期学術講演会","応用物理学会秋期学術講演会","2014-09-17","","jpn","oral_presentation","","","","","","","永久磁石内部では、高磁気異方性を有する強磁性結晶粒の粒間に、希土類元素やその酸化物を含む複雑な構造の非磁性層が挟まれた構造が形成されており、そこにおける粒間磁気結合は磁石特性に大きく影響し得る因子である。そのような構造を単純化およびモデル化した、Co/Tb/CoやFeB/Nd/FeBなどの積層膜を作製し、層間磁気結合を評価した。Co/Tb/Coにおいて、振動的な交換磁気結合に起因すると思われる飽和磁場や残留磁化の振舞が見出された。今後、界面の合金化や界面磁気異方性についても検討する必要がある。" "Development of lattice constant tunable spinel-based tunnel barriers","格子定数制御可能なスピネル系トンネルバリアの開発","介川 裕章","介川 裕章","シンポジウム「スピントロニクス材料・デバイスの最前線」","シンポジウム「スピントロニクス材料・デバイスの最前線」","2014-09-17","","jpn","oral_presentation","","","","","","","2014年第75回応用物理学会秋季学術講演会、スピントロニクス・マグネティクス分科のシンポジウム「スピントロニクス材料・デバイスの最前線」において、新スピントロニクス用トンネルバリア材料スピネルバリアについての招待講演を行う。" "Lattice-matched magnetic tunnel junctions using Heusler alloy Co2FeAl and spinel Mg-Al-O barrier","ホイスラー合金Co2FeAlとスピネルMg-Al-O バリアを用いた格子整合強磁性トンネル接合","介川 裕章, シェーク トーマス, 古林 孝夫, 温 振超, 猪俣 浩一郎, 三谷 誠司","介川 裕章, シェーク トーマス, 古林 孝夫, 温 振超, 猪俣 浩一郎, 三谷 誠司","第38回日本磁気学会学術講演会","第38回日本磁気学会学術講演会","2014-09-02","","jpn","oral_presentation","","","","","","","ホイスラー合金を用いた強磁性トンネル接合(MTJ)の室温におけるトンネル磁気抵抗(TMR)比は一般的な構造であるCoFeB/MgO/CoFeB系MTJの最大値に比べまだ小さく、その向上が求められている。一般的にMgOとCo基ホイスラー合金との格子不整合は数%と無視できない程度に大きく、MgO界面近傍に多数の欠陥が導入されることによりハーフメタル特性を引き出すことが容易ではない。また、ホイスラー合金の表面は活性であるため、酸化物バリア形成時に容易に酸化されやすく、バリア層との界面を理想的に保つことが必要となる。これらの問題の解決を目指して、本研究では格子定数がMgOよりも小さいスピネル系トンネルバリア(Mg-Al-O)を用いて高品質な格子整合ホイスラーMTJの作製を行った。ホイスラー合金には、Co2FeAl(CFA)を用い、Mg-Al-O層とCFA層間にCoFe層を挿入することでバリア界面の構造の調整も図った。" "Novel approach to investigate spin-polarization in half-metallic Heusler compounds via anisotropic magnetoresistance effect","異方性磁気抵抗効果を介したハーフメタルホイスラー合金のスピン偏極率評価","桜庭 裕弥, 平山 悠介, 古林 孝夫, 高橋 有紀子, 介川 裕章, 宝野 和博","桜庭 裕弥, 平山 悠介, 古林 孝夫, 高橋 有紀子, 介川 裕章, 宝野 和博","The 6th International Nanoelectronics Conference 2014","The 6th International Nanoelectronics Conference 2014","2014-07-28","","jpn","oral_presentation","","","","","","","近年、ホイスラー合金ハーフメタルを利用したCPP-GMR素子が次世代リードセンサーとして注目を集めているが、磁気抵抗比の改善等の多くの課題がまだ残されている。AMR効果を利用したハーフメタルホイスラー合金のスピン偏極率評価は極めて簡便な手法として利用することができ、材料の特性特性評価に有用である。Co2FeZやCo2MnZ系薄膜のAMR効果について最近の研究成果について講演を行う。" "Interface perpendicular magnetic anisotropy in magnetic nanostructures","磁性体ナノ構造における界面垂直磁気異方性","三谷 誠司, 具 正祐, 温 振超, 介川 裕章","三谷 誠司, 具 正祐, 温 振超, 介川 裕章","磁気記録・情報ストレージ研究会","磁気記録・情報ストレージ研究会","2014-07-17","","jpn","oral_presentation","","","","","","","強磁性金属と酸化物を積層した磁性体ナノ構造における界面垂直磁気異方性について、その研究動向などを概説する。スピントロニクス分野での界面垂直磁気異方性の応用の可能性や、現象の基礎的理解における今後の研究展開についても言及する。" "Spin-transfer torque switching in an Mg-Al-O based magnetic tunnel junction","Spin-transfer torque switching in an Mg-Al-O based magnetic tunnel junction","介川 裕章, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","IEEE International Magnetics Conference, INTERMAG Europe 2014","IEEE International Magnetics Conference, INTERMAG Europe 2014","2014-05-04","","jpn","oral_presentation","","","","","","","エピタキシャル成長したスピネルMg-Al-Oバリアを有する強磁性トンネル接合の作製を高度化し、スピネルバリアの低抵抗化を行いスピン注入磁化反転を実現したことを報告する。" "Quantitative analysis of AMR effect in half-metallic Heusler compounds films : comparison with magneto-transport in CPP-GMR devices","ハーフメタルホイスラー合金薄膜におけるAMR効果の定量解析 : CPP-GMR素子の磁気伝導特性との比較","桜庭 裕弥, 古林 孝夫, リ ソンテン, 高橋 有紀子, 宝野 和博, 介川 裕章","桜庭 裕弥, 古林 孝夫, リ ソンテン, 高橋 有紀子, 宝野 和博, 介川 裕章","IEEE International Magnetics Conference (INTERMAG 2014)","IEEE International Magnetics Conference (INTERMAG 2014)","2014-05-04","","jpn","oral_presentation","","","","","","","In this study, we have analyzed not only signs but also the magnitude of AMR in various Heusler compounds such as Co2FeGa0.5Ge0.5 (CFGG) and Co2MnGa0.25Ge0.75. Interestingly, we have found out a good quantitative agreement between AMR in Heusler films and MR in CPP-GMR devices. This work has shown that the ARM values can be used as a facile way to search for highly spin polarized ferromagnetic materials at ambient temperature." "Growth and characterisation of Heusler alloys","Growth and characterisation of Heusler alloys","介川 裕章","介川 裕章","1st EU-Japan Joint Workshop on "HARFIR"","1st EU-Japan Joint Workshop on "HARFIR"","2014-05-04","","jpn","oral_presentation","","","","","","","JST-EC DG RTD共同プロジェクト“Development of New Materials for the Substitution of Critical Metals"(日欧国際プロジェクト)における"Heusler Alloy Replacement for Iridium (HARFIR)"プロジェクト主催ワークショップにおいて招待講演を行う。最近のホイスラー合金を用いた高性能トンネル接合など最新のスピントロニクス素子に関する研究を講演する。 " "Perpendicular magnetic anisotropy in ultrathin ferromagnetic layer/tunnel barrier interfaces","Perpendicular magnetic anisotropy in ultrathin ferromagnetic layer/tunnel barrier interfaces","三谷 誠司, 具 正祐, 介川 裕章, 葛西 伸哉, 温 振超","三谷 誠司, 具 正祐, 介川 裕章, 葛西 伸哉, 温 振超","14th REIMEI Workshop on Spin Currents and Related Phenomena","14th REIMEI Workshop on Spin Currents and Related Phenomena","2014-02-09","","jpn","oral_presentation","","","","","","","Perpendicular magnetic anisotropy (PMA) in ultrathin ferromagnetic layer/tunnel barrier interfaces attracts growing interest since a variety of phenomena in spintronics, such as efficient spin-transfer-torque magnetization switching in perpendicularly magnetized tunnel junctions (p-MTJs), electric field control of anisotropy and current-driven dynamics in chiral domain walls, arise associated with the PMA in such interfaces. In addition, a lot of effort is being made for developing higher PMA in magnetic tunnel junctions, which is indispensable for high density magnetic random access memories. In my talk, our recent results on PMA in ultrathin ferromagnetic layer/tunnel barrier interfaces and spin-dependent transport in full p-MTJ stacks: In Fe(0.7nm)/MgO bilayers grown on Cr(100), PMA in " "Interface-induced perpendicular magnetic anisotropy in magnetic tunnel junctions with a Heusler alloy layer","ホイスラー合金を用いた強磁性トンネル接合と界面誘起垂直磁気異方性","介川 裕章, 温 振超, 猪俣 浩一郎, 三谷 誠司","介川 裕章, 温 振超, 猪俣 浩一郎, 三谷 誠司","第56回ナノマグネティクス専門研究会","第56回ナノマグネティクス専門研究会","2013-11-29","","jpn","oral_presentation","","","","","","","ホイスラー合金Co2FeAlを用いた強磁性トンネル接合の最近の研究について講演を行った。また、MgOとCo2FeAl超薄膜の積層構造において観察された強い膜面垂直磁気異方性についての研究紹介を行った。" "Interface perpendicular magnetic anisotropy in magnetic tunnel junctions","Interface perpendicular magnetic anisotropy in magnetic tunnel junctions","三谷 誠司, 具 正祐, 温 振超, 介川 裕章","三谷 誠司, 具 正祐, 温 振超, 介川 裕章","International Japanese-French workshop on Spintronics","International Japanese-French workshop on Spintronics","2013-11-28","","jpn","oral_presentation","","","","","","","Perpendicularly magnetized magnetic tunnel junction is indispensable for high-density magnetic random access memories, and therefore perpendicular magnetic anisotropy (PMA) at the interfaces between MgO tunnel barrier and ferromagnetic materials such as CoFeB has attracted much attention. Recently, we have observed PMA as large as Ku=1.4x10^7 erg/cm3 for an interface-engineered Fe/MgO interface and found that by using MCD measurements, even for Co-based Heusler alloy Co2FeAl, Fe atoms play a crucial role for appearance of the large interface PMA." "Preparation of epitaxial NiFe(111)/AlOx ultrathin bilayer structures for a high-efficiency spin injector ","Preparation of epitaxial NiFe(111)/AlOx ultrathin bilayer structures for a high-efficiency spin injector ","三谷 誠司, 具 正祐, 介川 裕章","三谷 誠司, 具 正祐, 介川 裕章","58th Annual Conference on Magnetism and Magnetic Materials","58th Annual Conference on Magnetism and Magnetic Materials","2013-11-04","","jpn","oral_presentation","","","","","","","強磁性トンネル接合はMRAMの中心素子であり、その高性能化が重要開発課題となっている。これまでの強磁性トンネル接合は、主にbcc合金の(100)成長に基づいており、これが一つの拘束条件となると同時に、磁気ヘッドでの技術的蓄積のあるfcc(111)合金の使用の障碍となっている。本研究では、fcc(111)合金を用いた強磁性トンネル接合の基盤技術となるfcc(111)用結晶化バリアの成長を実現し、同時に成長制御の鍵となる成膜パラメータを明らかにした。" "Giant tunnel magnetoresistance at room temperature in a cubic monocrystallne Al2O3-based magnetic tunnel junction","Giant tunnel magnetoresistance at room temperature in a cubic monocrystallne Al2O3-based magnetic tunnel junction","介川 裕章, 猪俣 浩一郎, 三谷 誠司","介川 裕章, 猪俣 浩一郎, 三谷 誠司","58th Annual Magnetism and Magnetic Materials (MMM) Conference","58th Annual Magnetism and Magnetic Materials (MMM) Conference","2013-11-04","","jpn","oral_presentation","","","","","","","Tunnel magnetoresistance (TMR) ratios for amorphous alumina Al2O3-based magnetic tunnel junctions (MTJs) do not exceed 70-80% at room temperature (RT) due to an incoherent tunneling process. We recently developed a monocrystalline Al2O3 ultrathin barrier using a post-oxidation of an Al layer on an epitaxial Fe(001) layer, and the Al2O3 was found to be a metastable γ-phase with a cubic symmetry. We also demonstrated an enhanced TMR up to 102% at RT for an Fe/epitaxial Al2O3/Fe MTJ. This indicates that the monocrystallne Al2O3 could be a candidate for an alternative coherent tunnel barrier as well as MgO and MgAl2O4. However, the TMR ratio of the Fe/epitaxial Al2O3/Fe MTJ was still much smaller than that reported in an Fe/MgO/Fe MTJ and an Fe/MgAl2O4/Fe MTJ . Here, we report a giant TMR ra" "Giant tunnel magnetoresistance in perfectly lattice-matched magnetic tunnel junctions -current status of spinel MgAl2O4-based tunnel barriers-","完全格子整合した磁気トンネル接合の巨大トンネル磁気抵抗効果 〜スピネルMgAl2O4系バリアの現状〜","介川裕章","介川裕章","磁気記録・情報ストレージ研究会(MR)・マルチメディアストレージ研","磁気記録・情報ストレージ研究会(MR)・マルチメディアストレージ研","2013-10-24","","jpn","oral_presentation","","","","","","","強磁性層/トンネルバリア/強磁性層構造を有する強磁性トンネル接合(MTJ)は、不揮発性磁気メモリ素子やハードディスクドライブのヘッドセンサーの基本動作を担っている。本研究ではMTJの新しいバリア層材料として結晶質のMgAl2O4(スピネル)が有望であることを報告する。MgAl2O4バリアを用いることで接合界面に欠陥を含まない完全格子整合した界面が実現され、室温トンネル磁気抵抗比(TMR)比の増大効果を示すことや、TMR比のバイアス電圧依存性の向上が可能であることを示す。さらに,MgAl2O4のもつスピネル構造の陽イオン位置を不規則化させることでTMR比が飛躍的に増大することを明らかにし,室温300%以上の巨大なTMR比を達成した。" "Fabrication of pseudo-spin-MOSFETs using a multi-project wafer CMOS chip","Fabrication of pseudo-spin-MOSFETs using a multi-project wafer CMOS chip","R. Nakane, Y. Shuto, 介川 裕章, 温 振超, S. Yamamoto, 三谷 誠司, M. Tanaka, 猪俣 浩一郎, S. Sugahara","R. Nakane, Y. Shuto, 介川 裕章, 温 振超, S. Yamamoto, 三谷 誠司, M. Tanaka, 猪俣 浩一郎, S. Sugahara","43rd European Solid-State Device Research Conference","43rd European Solid-State Device Research Conference","2013-09-16","","jpn","oral_presentation","","","","","","","We demonstrate monolithic integration of pseudo-spin-MOSFETs (PS-MOSFETs) using vendor-made MOSFETs fabricated in a low-cost multi-project wafer (MPW) product and lab-made magnetic tunnel junctions (MTJs) formed on the topmost passivation film of the MPW chip. The tunneling magnetoresistance (TMR) ratio of the fabricated MTJs exhibits a sufficiently large TMR ratio (> 140 %) adaptable to the PS-MOSFET application. The implemented PS-MOSFETs show clear modulation of the output current controlled by the magnetization configuration of the MTJs, and a maximum magnetocurrent ratio of 90 % was achieved. " "Giant tunnel magnetoresistance in a fully epitaxial Fe/Al2O3/Fe tunnel junction","Giant tunnel magnetoresistance in a fully epitaxial Fe/Al2O3/Fe tunnel junction","介川 裕章, 猪俣 浩一郎, 三谷 誠司","介川 裕章, 猪俣 浩一郎, 三谷 誠司","2013年 第74回応用物理学会秋季学術講演会","2013年 第74回応用物理学会秋季学術講演会","2013-09-16","","jpn","oral_presentation","","","","","","","Alumina (Al2O3) tunnel barriers for magnetic tunnel junctions (MTJs) have been believed to be in an amorphous state since the demonstrations of large tunnel magnetoresistance (TMR) at room temperature (RT). However, TMR ratios for amorphous Al2O3-based MTJs were limited to only 70-80% at RT due to an incoherent tunneling process. We recently developed a monocrystalline Al2O3 barrier with a cubic symmetry (metastable gamma-Al2O3) using a post-oxidation process of an Al layer prepared on an Fe(001) layer. We also demonstrated an enhanced TMR up to 102% at RT for an Fe/gamma-Al2O3/Fe MTJ. This indicates that the monocrystallne gamma-Al2O3 could be a candidate for an alternative coherent tunnel barrier. However, the obtained TMR ratio was still much smaller than that reported in an Fe/MgO/Fe M" "Enhanced perpendicular magnetic anisotropy in Co2FeAl full-Heusler alloy magnetic tunnel junctions with a Ru buffer","Enhanced perpendicular magnetic anisotropy in Co2FeAl full-Heusler alloy magnetic tunnel junctions with a Ru buffer","介川 裕章, 温 振超, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 温 振超, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","2013年 第74回応用物理学会秋季学術講演会","2013年 第74回応用物理学会秋季学術講演会","2013-09-16","","jpn","oral_presentation","","","","","","","Recently, perpendicular magnetic anisotropy (PMA) arising at the interface between a ferromagnetic metal (FM) and an oxide barrier is actively being investigated, which has attracted much attention not only for the magnetoresistive random access memories (MRAMs) applications but also for spintronic devices with electric field or voltage controlled magnetization switching [1-4]. In this work, we report an enhanced PMA and tunnel magnetoresistance (TMR) in Co2FeAl (CFA) full-Heusler alloy based perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with a ruthenium (Ru) buffer deposited on an MgO(001) single crystal substrate, which can be a candidate for p-MTJ using the Co-based full-Heusler alloy with high spin polarization and potentially low magnetic damping." "Magnetic tunnel junctions with an Mg-Al-O barrier","Mg-Al-Oバリアを有する強磁性トンネル接合","介川 裕章, 猪俣 浩一郎, 三谷 誠司","介川 裕章, 猪俣 浩一郎, 三谷 誠司","第37回 日本磁気学会学術講演会","第37回 日本磁気学会学術講演会","2013-09-02","","jpn","oral_presentation","","","","","","","我々はこれまでスピネルMgAl2O4をベースとした結晶質バリア層の作製を強磁性電極上に実現し、TMRの増大効果の発見や格子定数の制御による完全格子整合MTJ構造を実現した。興味深いことに、MgAl2O4が完全なスピネル構造であるよりも、カチオンサイトの不規則性が導入されている不規則化スピネル構造においてより高いTMR比が得られる。この不規則化スピネルバリアの実現によって室温で最大308%の巨大TMR比(CoFe/Mg-Al-O /CoFe構造)を達成している。本研究では、このカチオン不規則化スピネルバリアの作製方法やバリア層膜厚によるTMR特性への影響を報告する。" "Giant tunnel magnetoresistance in MgAlOx-based magnetic tunnel junctions","Giant tunnel magnetoresistance in MgAlOx-based magnetic tunnel junctions","介川 裕章, 新関 智彦, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 新関 智彦, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","JSPS York-Tohoku Research Symposium on Magnetic Materials and Sp","JSPS York-Tohoku Research Symposium on Magnetic Materials and Sp","2013-06-10","","jpn","oral_presentation","","","","","","","Tunnel magnetoresistance (TMR) devices with a monocrystalline MgAl2O4 barrier were successfully developed. The lattice matched heterostructure without any defects at the barrier interfaces was obtained, and TMR enhancement due to a spin-dependent coherent tunneling effect was demonstrated in the structure. In addition, it was found that cation-site disordering into the MgAl2O4 structure significantly increases the TMR. In fact, a giant TMR over 300% at room temperature was achieved by introducing the disordering into the barrier. These results demonstrate the effectiveness of MgAl2O4 as a spintronics material." "Spin-transfer magnetization switching and interface perpendicular magnetic anisotropy in Heusler alloy-based magnetic tunnel junctions","Spin-transfer magnetization switching and interface perpendicular magnetic anisotropy in Heusler alloy-based magnetic tunnel junctions","三谷 誠司, 介川 裕章, 温 振超, 葛西 伸哉, 猪俣 浩一郎","三谷 誠司, 介川 裕章, 温 振超, 葛西 伸哉, 猪俣 浩一郎","York Tohoku Symposium on Magnetic materials and Spintronic devic","York Tohoku Symposium on Magnetic materials and Spintronic devic","2013-06-10","","jpn","oral_presentation","","","","","","","Co-based full-Heusler alloys such as Co2FeAl are of particular interest because of their high spin polarizations and low magnetic damping constants, which are quite useful for magnetic tunnel junction (MTJ)-based spintronic applications. In this talk, our recent results on spin transfer torque magnetization switching [1] and interface perpendicular magnetic anisotropy (PMA) [2,3] in Co2FeAl-based MTJs will be presented, highlighting the enhancement of interface PMA in Co2FeAl-based MTJs with a Ru buffer layer. Some related topics will also be provided shortly." "Plasma-assisted crystallization of tunnel barriers: A new route for fabricating epitaxial magnetic tunnel junctions","Plasma-assisted crystallization of tunnel barriers: A new route for fabricating epitaxial magnetic tunnel junctions","三谷 誠司, 具 正祐, 介川 裕章","三谷 誠司, 具 正祐, 介川 裕章","International Symposium on Metallic Multilayers","International Symposium on Metallic Multilayers","2013-05-20","","jpn","oral_presentation","","","","","","","結晶性トンネルバリアを有する強磁性トンネル接合では、コヒーレントトンネル効果による大きなTMRなどの顕著なスピン依存伝導効果が観測される。基礎的な重要性に加え、MRAM応用などにおいても注目されるものである。本研究では、従来結晶性バリアが得られないと思われてきた材料系について、プラズマ処理によるバリアの結晶化を試みた。300˚C程度の低温アニールとの組合せによって、一旦アモルファスとして成長したMgAl2O4等のバリア層を結晶化させることに成功した。" "Perpendicular magnetic anisotropy of ultra thin Fe(100) layers capped with MgAl2Ox, Al2Ox, MgO and C60 over layers","Perpendicular magnetic anisotropy of ultra thin Fe(100) layers capped with MgAl2Ox, Al2Ox, MgO and C60 over layers","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 猪俣 浩一郎, 圓谷志郎, 松本 吉弘, 境 誠司","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 猪俣 浩一郎, 圓谷志郎, 松本 吉弘, 境 誠司","International Symposium on Metallic Multilayers","International Symposium on Metallic Multilayers","2013-05-20","","jpn","oral_presentation","","","","","","","MRAM応用等の基盤技術となる垂直磁気異方性に関して、強磁性超薄膜層と酸化物等の界面に生じる界面垂直磁気異方性について研究をおこなった。従来より知られているMgOにおける界面磁気異方性と同程度の異方性が、成長条件を適正化することによってMgAl2OxやAl2Oxについても得られた。更には、分子性炭素材料であるC60層を用いた場合にも垂直磁気異方性を得ることができた。" "Perpendicular magnetic anisotropy of Fe/MgO interfaces for magnetic tunnel junctions with out-of-plane magnetizations","強磁性トンネル接合のためのFe/MgO界面の垂直磁気異方性","具 正祐, 三谷 誠司, 介川 裕章, 温 振超","具 正祐, 三谷 誠司, 介川 裕章, 温 振超","第60回応用物理学会春季学術講演会","第60回応用物理学会春季学術講演会","2013-03-27","","jpn","oral_presentation","","","","","","","We have optimized preparation conditions for Fe/MgO structures and have achieved a very large perpendicular magnetic anisotropy (PMA) of 14 Merg/cm3, which is somewhat close to the theoretically calculated value. In addition, we have attempted to prepare a p-MTJ with the huge PMA of Fe/MgO. TMR and resistance area (RA) products are characterized by current-in-plane tunneling (CIPT) measurement, and a small TMR ratio is obtained for an as-prepared MTJ sample, and the TMR ratio is increased by appropriate post-annealing processes as well as PMA. " "Giant tunnel magnetoresistance and coherent tunneling effect in epitaxial MgAl2O4-based tunnel junctions","Giant tunnel magnetoresistance and coherent tunneling effect in epitaxial MgAl2O4-based tunnel junctions","介川 裕章","介川 裕章","International Symposium On Computational Science 2013","International Symposium On Computational Science 2013","2013-02-18","","jpn","oral_presentation","","","","","","","The giant tunnel magnetoresistance (TMR) effect due to the coherent tunneling of highly spin-polarized electrons though the delta1 state in MgO-based magnetic tunnel junctions (MTJs) has accelerated the application to magnetoresistive random access memories and read heads in hard disk drives. The spinel MgAl2O4 (spinel structure) is advantageous to an alternative tunnel barrier material of coherent MTJs because of its nondeliquescency and its small lattice mismatch with typical bcc-CoFe alloys and Co-based Heusler alloys (< 1%). In this study, we report a giant TMR ratio in MgAl2O4-based MTJs with a cation-site (Mg2+ and Al3+ sites of spinel) disorder structure (cation-disorder spinel)." "Epitaxial magnetic tunnel junctions with a nomocrystalline Al2O3 barrier","Epitaxial magnetic tunnel junctions with a nomocrystalline Al2O3 barrier","介川 裕章, 三谷 誠司, 新関 智彦, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 三谷 誠司, 新関 智彦, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","The 12th Joint MMM/Intermag Conference","The 12th Joint MMM/Intermag Conference","2013-01-14","","jpn","oral_presentation","","","","","","","Al2O3 tunnel barrier for magnetic tunnel junctions (MTJs) has been believed to be amorphous since the first demonstrations of large tunnel magnetoresistance (TMR) effect at room temperature (RT). Unlike crystalline MgO-based MTJs, an upper limit of TMR ratio for Al2O3-based MTJs was only 70-80% at RT. We recently developed a nomocrystalline MgAl2O4 barrier with spinel structure and demonstrated an enhanced TMR of 117% at RT for an Fe/MgAl2O4/Fe MTJ. If a monocrystalline Al2O3 barrier can be achieved on a metallic layer as well as MgAl2O4, Al2O3 will become a promising tunnel barrier for future spintronics devices." "Spin current induced ferromagnetic resonance in ferromagnetic/non-magnetic bi-layer thin films","強磁性/非磁性二層膜におけるスピン流誘起強磁性共鳴","葛西 伸哉, 近藤 浩太, 介川 裕章, 三谷 誠司, 塚越 一仁","葛西 伸哉, 近藤 浩太, 介川 裕章, 三谷 誠司, 塚越 一仁","ICAUMS2012","ICAUMS2012","2012-10-02","","jpn","oral_presentation","","","","","","","近年、スピントロニクス分野においてスピン流の生成と制御が大きな注目を集めている。スピンホール効果は電流からスピン流の生成を可能とする新奇現象であり、その変換効率であるスピンホール角の定量評価は重要な課題である。本講演ではスピン流誘起強磁性共鳴法を用いた、スピンホール角の評価について報告する。特にスピンホール角の材料依存性、強磁性ー非磁性材料の組み合わせによる重畳効果の存在、また、直流電流の印加による大きなダンピング変調について紹介をする。" "Enhanced tunnel magnetoresistance in magnetic tunnel junctionswith a cubic Mg-Al-O barrier","Enhanced tunnel magnetoresistance in magnetic tunnel junctionswith a cubic Mg-Al-O barrier","介川 裕章, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","International Conference of AUMS (ICAUMS2012)","International Conference of AUMS (ICAUMS2012)","2012-10-02","","jpn","oral_presentation","","","","","","","The spinel MgAl2O4 (spinel structure) is advantageous to a tunnel barrier of magnetic tunnel junctions (MTJs) because of its nondeliquescency and its small lattice mismatch with typical bcc-Fe(Co) alloys and Co-based Heusler alloys (~ 1%). Therefore an achievement of perfect lattice-matched structure with defect-free barrier interfaces is expected in MgAl2O4-based MTJs. We recently reported a relatively large tunnel magnetoresistance (TMR) of 117% at room temperature (RT) and 165% at 16 K in an epitaxial Fe/spinel MgAl2O4/Fe(001) MTJ. However the obtained TMR was still small for practical applications. In this study we fabricated CoFe/MgAl-Ox/CoFe MTJs and achieved a larger TMR (over 300% at RT) using an off-stoichiometric Mg-Al-O barrier." "Detection of spin-current induced ferromagnetic resonance in nonmagnetic/ferromagnetic junction ","非磁性/強磁性接合におけるスピン流誘起強磁性共鳴の検出:材料依存性","近藤 浩太, 介川 裕章, 塚越 一仁, 三谷 誠司, 葛西 伸哉","近藤 浩太, 介川 裕章, 塚越 一仁, 三谷 誠司, 葛西 伸哉","2012年日本物理学会秋季大会","2012年日本物理学会秋季大会","2012-09-18","","jpn","oral_presentation","","","","","","","近年、スピンホール効果におけるスピンホール角を定量評価するための手法として、非磁性/強磁性接合系におけるスピン流誘起強磁性共鳴の測定が注目されている。本講演では強磁性体としてPermalloy(Fe-Ni合金)、およびCoFe合金、非磁性体としてPt, Taを用いた二層膜における、Ptのスピンホール角とスピン拡散長の評価について報告する。特にCoFe-Ta系ではスピンホール角の評価に大きな異常が現れており、スピンホール角の定量的な評価が困難であることが分かった。その原因としては、ラッシュバ効果や界面誘導磁気異方性など界面起源の現象の重畳が考えられる。" "Phase transition of spinel tunnel barriers","スピネル系トンネルバリアの相変化","三谷 誠司, 具 正祐, 介川 裕章","三谷 誠司, 具 正祐, 介川 裕章","応用物理学会学術講演会","応用物理学会学術講演会","2012-09-11","","jpn","oral_presentation","","","","","","","強磁性トンネルバリアの相の安定性と結晶化法について実験結果を得た。MgAl2O4、Al2O3等のバリア材のアモルファス状態は安定度の高い準安定相であるが、加熱とプラズマ処理によって容易に結晶化できることを見いだした。Al2O3を用いた界面磁気異方性の大きさについても評価を行った。" "Tunnel magnetoresistance and spin-transfer magnetization switching in CoFe/Mg-Al-Ox/CoFe magnetic tunnel junctions","CoFe/Mg-Al-Ox/CoFe接合のトンネル磁気抵抗効果とスピン注入磁化反転","介川 裕章, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","2012年 秋季 第73回応用物理学会学術講演会","2012年 秋季 第73回応用物理学会学術講演会","2012-09-11","","jpn","oral_presentation","","","","","","","スピネル構造を有するMgAl2O4 はbcc-CoFe 合金やCo 基ホイスラー合金などと格子不整合が1%以下と小さく,また,潮解性を持たないため,強磁性トンネル接合(MTJ)の新規バリア材料として有望である。我々は,これまでエピタキシャルMgAl2O4 バリアとFe 電極を用いて,室温117%の比較的大きなトンネル磁気抵抗(TMR)比と小さいバイアス電圧依存性を報告した。しかし,実用のためには更に高いTMR 比が求められる上,スピン注入磁化反転の実現も必要となる。本研究では,bcc-CoFe 電極を用いたMg-Al-Ox バリアMTJ の作製を通して,巨大TMR およびスピン注入磁化反転の実現を目指した。" "Enhanced perpendicular magnetic anisotropy in Fe/(MgAl2)OX bilayer structures with interface optimization processes","Enhanced perpendicular magnetic anisotropy in Fe/(MgAl2)OX bilayer structures with interface optimization processes","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","International Conference on Magnetism","International Conference on Magnetism","2012-07-08","","jpn","oral_presentation","","","","","","","Ferromagnetic metals (FM) electrodes with large perpendicular magnetic anisotropy (PMA) are actively being investigated. Recently PMA arising at the interface between a FM and an oxide layer such as CoFeB/MgO and Co2FeAl/MgO were reported. The PMA at which between FMs and oxide barrier materials has attracted much attention not only for the STT-MRAM applications but also for spintronic devices with electric field control of magnetization. We report the enhanced PMA in Fe/MgAl2OX structures with the effective perpendicular magnetic anisotropy energy density (Keff) ~ 3 erg/cm3. In the case of an Fe layer with a crystalline (MgAl2)OX layer, it exhibited perpendicular magnetization characteristics, and the value of Keff was increased from ~ 0 to ~3 erg/cm3 with increasing annealing temperature" "Enhanced tunnel magnetoresistance in magnetic tunnel junctions with an epitaxial Mg-Al-O barrier","Enhanced tunnel magnetoresistance in magnetic tunnel junctions with an epitaxial Mg-Al-O barrier","介川 裕章, 三谷 誠司, 新関 智彦, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 三谷 誠司, 新関 智彦, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","The 19th International Conference on Magnetism (ICM2012)","The 19th International Conference on Magnetism (ICM2012)","2012-07-08","","jpn","oral_presentation","","","","","","","In this study we achieved a fully epitaxial CoFe/Mg-Al-O/CoFe(001) magnetic tunnel junction (MTJ) using a sputter deposition and a plasma oxidation of Mg-Al alloy layers. We demonstrated the very large TMR ratio of 308% at RT in the MTJ even though the barrier layer had an off-stoichiometric MgAl2O4 composition (Mg40Al60-Ox). This result suggests that Mg-Al-O is promising for a tunnel barrier of future spintronics devices using coherent tunneling." "Tunneling magnetoresistance in perpendicular magnetized Co2FeAl/MgO/CoFeB magnetic tunnel junctions","Tunneling magnetoresistance in perpendicular magnetized Co2FeAl/MgO/CoFeB magnetic tunnel junctions","温 振超, 介川 裕章, 葛西 伸哉, 林 将光, 三谷 誠司, 猪俣 浩一郎","温 振超, 介川 裕章, 葛西 伸哉, 林 将光, 三谷 誠司, 猪俣 浩一郎","International Conference on Magnetism","International Conference on Magnetism","2012-07-08","","jpn","oral_presentation","","","","","","","The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy thin film in the structures of CFA/MgO with the high Ku of 2-3x10^6 erg/cm^3. The CFA thickness dependence of Ku was investigated at different annealing temperatures, indicating that the perpendicular anisotropy of CFA is contributed by the interfacial anisotropy between CFA and MgO. Furthermore, we fabricated perpendicularly magnetized tunnel junctions (p-MTJs) using CFA full-Heusler alloy. The out-of-plane tunneling magnetoresistance (TMR) ratio of 53% at room temperature was observed in CFA/MgO/Co20Fe60B20 p-MTJs on Cr-buffered MgO(001) substrates. By inserting 0.1 nm Fe (Co50Fe50) between MgO and Co20Fe60B20, TMR ratio was significantly enhanced to 91% (82%) due to the improved interface. " "Full Heusler Co2FeAl thin films for perpendicular magnetic tunnel junctions","垂直磁化型強磁性トンネル接合の実現のためのフルホイスラー合金Co2FeAl薄膜","介川 裕章, 温 振超, 葛西 伸哉, 林 将光, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 温 振超, 葛西 伸哉, 林 将光, 三谷 誠司, 猪俣 浩一郎","The 9th RIEC International Workshop on Spintronics","The 9th RIEC International Workshop on Spintronics","2012-05-31","","jpn","oral_presentation","","","","","","","Since full-Heusler alloys typically have low magnetocrystalline anisotropy due to their cubic crystalline structure, the achievement of perpendicular magnetic anisotropy (PMA) in full Heusler alloy films is challenging. Nevertheless, we recently demonstrated the PMA of ultra-thin CFA in a CFA(< 1 nm)/MgO structure due to the large interface magnetic anisotropy. The perpendicular anisotropy energy (Ku) of the CFA layer was 2–3×106 erg/cm3, comparable to that of CoFeB/MgO structure. In addition, we successfully fabricated perpendicularly magnetized MTJs with a structure of CFA/MgO/CoFeB." "In situ characterization of growth and crystalline process of spinel MgAl2O4 tunnel barriers on Fe(100)","Fe(100)上のスピネルMgAl2O4トンネルバリアの成長と結晶化のその場観察","三谷 誠司, 介川 裕章, 具 正祐","三谷 誠司, 介川 裕章, 具 正祐","Intermag 2012","Intermag 2012","2012-05-07","","jpn","oral_presentation","","","","","","","スピントロニクス分野のキーデバイスである強磁性トンネル接合用の新規バリア材料MgAl2O4について、成長過程と結晶化を反射高速電子線回折のその場観察によって研究した。わずかな条件の相違で結晶化の有無が変化することが分かり、また、一度非晶質で成長したバリアを後からプラズマ酸化で結晶化させることもできた。その他、高品位の強磁性トンネル接合の作製に関する有益な知見を得た。" "Current-induced magnetization switching in epitaxial full-Heusler Co2FeAl-based magnetic tunnel junctions","Current-induced magnetization switching in epitaxial full-Heusler Co2FeAl-based magnetic tunnel junctions","介川 裕章, 温 振超, 近藤 浩太, 葛西 伸哉, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 温 振超, 近藤 浩太, 葛西 伸哉, 三谷 誠司, 猪俣 浩一郎","INTERMAG2012","INTERMAG2012","2012-05-07","","jpn","oral_presentation","","","","","","","In this study, we demonstrate CIMS in epitaxial CFA-based MTJs. The following two MTJ structures were prepared on a Cr-buffered MgO(001) substrate using magnetron sputtering; (i) CFA (1.5)/Mg (0.20)/MgO (0.36)/Co50Fe50 (4.0)/Ir20Mn80 (13)/cap (CFA-free MTJ) and (ii) CFA (30)/Mg (0.20)/MgO (0.63)/Co20Fe60B20 (2.0)/cap (CFA-reference MTJ) (numbers in parentheses are thickness in nm). " "RHEED observation and interfacial perpendicular magnetic anisotropy in MgAl2O4 tunnel barrier layers","MgAl2O4トンネルバリア層の形成過程のRHEED観察と界面垂直磁気異方性の評価","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","日本金属学会2012年春期(第150回)講演大会","日本金属学会2012年春期(第150回)講演大会","2012-03-28","","jpn","oral_presentation","","","","","",""," Spin-RAM等のメモリデバイスでは垂直磁化を有する強磁性トンネル接合の利用が必須となっており、最近、トンネルバリア層と強磁性金属電極の間に生じる界面垂直磁気異方性が注目されている。CoFeB/MgO界面において、一定の大きさの垂直磁気異方性が報告されており、スピン注入磁化反転の実証もなされているが、より大きな垂直磁気異方性を有する物質系の探索についてはほとんど報告例がない。本研究では、最近我々のグループで見いだされた結晶質の新しいトンネルバリア材料であるMgAl2O4を用いて界面垂直磁気異方性の探索を行った。その結果、形成されたMgAl2Ox層の構造は成長・酸化条件によって複雑に変化し、条件に応じて結晶相とアモルファス相を作り分けることができた。結晶相のMgAl2Oxバリア層を有する試料では明瞭な垂直磁化が得られた。 " "Preparation and interface perpendicular magnetic anisotropy of Fe/MgAl2O4 films","Fe/MgAl2Ox積層膜の作製と界面垂直磁気異方性の評価","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","日本物理学会第67回年次大会","日本物理学会第67回年次大会","2012-03-24","","jpn","oral_presentation","","","","","","","MRAMの高性能化に関して強磁性トンネル接合における界面垂直磁気異方性が注目されている。本研究では、既報の理論との比較が可能なFeを強磁性電極物質として選び、垂直磁気異方性の発現するトンネルバリアの探索を行った。その結果、新規にFe/MgAl2O4系において大きな垂直磁気異方性を見いだした。" "Spin-current induced ferromagnetic resonance in nonmagnetic/ferromagnetic bilayer thin films 2","非磁性/強磁性接合におけるスピン流誘起強磁性共鳴の検出II","近藤 浩太, 介川 裕章, 塚越 一仁, 三谷 誠司, 葛西 伸哉","近藤 浩太, 介川 裕章, 塚越 一仁, 三谷 誠司, 葛西 伸哉","日本物理学会67回年次大会","日本物理学会67回年次大会","2012-03-24","","jpn","oral_presentation","","","","","","","近年、スピントロニクス分野においてスピン流の生成と制御が大きな注目を集めている。スピンホール効果は電流からスピン流の生成を可能とする新奇現象であり、その変換効率であるスピンホール角の評価は重要な課題である。本講演ではスピン流誘起強磁性共鳴法を用いた、スピンホール角の評価について報告する。また、直流電流重畳による、緩和定数の制御についても報告を行う。強磁性体としてPermalloy、非磁性体としてPtを用いた二層膜におけるスピン流誘起強磁性共鳴スペクトルの解析から、Ptのスピンホール角Qとスピン拡散長Lはそれぞれ、 (Q,L)=(0.022, 1.2 nm)と評価された。これらの値は、直流電流重畳によるダンピング定数変調から評価される(Q,L)と同程度の値である。また、直流電流重畳によって、ダンピング定数は最大で50%以上の変調が可能であることが明らかとなった。本知見は、スピンホール効果を用いた発振素子実現の可能性を強く示唆している。" "Epitaxial magnetic tunnel junction with a metastable cubic Al2O3 barrier","準安定立方晶Al2O3を用いたエピタキシャル強磁性トンネル接合","介川 裕章, 三谷 誠司, 新関 智彦, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 三谷 誠司, 新関 智彦, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","2012年春季 第59回応用物理学関係連合講演会","2012年春季 第59回応用物理学関係連合講演会","2012-03-15","","jpn","oral_presentation","","","","","","","室温におけるトンネル磁気抵抗(TMR)の実現は,アモルファスAlOxをバリア層として用いた強磁性トンネル接合(MTJ)によって達成され,今日の磁気ランダムアクセスメモリ(MRAM)応用への大きな原動力となった。これまで,MTJ用に金属強磁性層上に作製されてきたAlOxバリア層はアモルファス構造であることが常識となっており,エピタキシャル成長したAlOxバリアは報告されていなかった。最近,著者らはエピタキシャル膜上にMg/Al酸化膜を作製することによって,スピネル型MgAl2O4エピタキシャルバリアが作製可能であることを報告してきた。本研究では,MgAl2O4バリア作製法をAl単層膜へ応用することで,結晶質Al2O3バリアを実現し,それによって良好なTMR特性が得られたため報告する。" "Perpendicular magnetic anisotropy in Fe/MgAl2OX structures","Fe/MgAl2OX構造における垂直磁気異方性","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","具 正祐, 三谷 誠司, 介川 裕章, 温 振超, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","応用物理学関係連合講演会","応用物理学関係連合講演会","2012-03-15","","jpn","oral_presentation","","","","","","","垂直磁化材料を用いた磁気トンネル接合は、高集積度のスピンRAMの開発に必要不可欠であり、現在種々の研究が進められている。本研究では、磁気トンネル接合の1部をなすFe/MgAl2Ox界面に垂直磁気異方性が発現するすることを見いだした。MgAl2Ox層の構造や界面の酸化状態によって磁気異方性が大きく変化するという結果も得ており、磁気異方性の発現機構や今後の特性改善に関して報告する。" "Current-induced magnetization switching in magnetic tunnel junctions with a full-Heusler Co2FeAl layer","フルホイスラー合金Co2FeAl層を有する強磁性トンネル接合におけるスピン注入磁化反転","介川 裕章, 温 振超, 近藤 浩太, 葛西 伸哉, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 温 振超, 近藤 浩太, 葛西 伸哉, 三谷 誠司, 猪俣 浩一郎","2012年春季 第59回応用物理学関係連合講演会","2012年春季 第59回応用物理学関係連合講演会","2012-03-15","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)におけるスピン注入磁化反転の電流密度の低減は,不揮発メモリMRAMや次世代不揮発ロジックへの応用のために非常に重要な課題である。MTJでのスピン注入磁化反転はほぼCoFeB/MgO/CoFeB系に限られており,他の材料系を用いた報告例は非常に少ないため,用いる材料の物性値と反転電流密度との関係はまだ明らかとはいえない。本研究では,高トンネル磁気抵抗(TMR)が実現でき,また,非常に磁気緩和定数が小さいことが報告されている,フルホイスラー合金Co2FeAl(CFA)に着目した。CFA層を反転層(CFA-Free)もしくは参照層(CFA-Ref)として有する2種類の低抵抗MTJ素子を作製し,それぞれのスピン注入磁化反転特性を評価した。" "Large tunnel magnetoresistance and perpendicular magnetization in full-Heusler alloy Co2FeAl thin films","フルホイスラーCo2FeAl合金を用いた巨大TMR比と垂直磁気異方性","介川 裕章, 温 振超, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 温 振超, 三谷 誠司, 猪俣 浩一郎","CREST「次世代デバイス」領域 第一回公開シンポジウム","CREST「次世代デバイス」領域 第一回公開シンポジウム","2011-11-25","","jpn","oral_presentation","","","","","","","フルホイスラー合金Co2FeAl(CFA)薄膜を用いた強磁性トンネル接合における巨大なTMR比について,またCFA極薄膜における垂直磁気異方性についての報告を行う。" "Perpendicular magnetization of Co2FeAl full-Heusler alloy thin films induced by MgO interface ","Perpendicular magnetization of Co2FeAl full-Heusler alloy thin films induced by MgO interface ","温 振超, 介川 裕章, 三谷 誠司, 猪俣 浩一郎","温 振超, 介川 裕章, 三谷 誠司, 猪俣 浩一郎","第35回 日本磁気学会学術講演会","第35回 日本磁気学会学術講演会","2011-09-27","","jpn","oral_presentation","","","","","","","Half-metallic full-Heusler alloys with a high spin polarization and a low damping constant are promising materials for the further reduction of the current density. Using Co2FeAl (CFA) as a kind of full-Heusler alloys, we have demonstrated a high tunneling spin polarization in magnetic tunnel junctions (MTJs), achieving a high tunneling magnetoresistance (TMR) of 360% at room temperature (RT). CFA is also known to possess a very low damping constant. In this study we report PMA properties of ultrathin CFA films." "Improvement of tunnel magnetoresistance and reduction of tunnel resistance in epitaxial CoFe/MgAl2O4/CoFe(001) tunnel junctions","エピタキシャルCoFe/MgAl2O4/CoFe(001)強磁性トンネル接合の高TMR化と低抵抗化","介川 裕章, 新関 智彦, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","介川 裕章, 新関 智彦, 三谷 誠司, 大久保 忠勝, 猪俣 浩一郎, 宝野 和博","第35回 日本磁気学会学術講演会 ","第35回 日本磁気学会学術講演会 ","2011-09-27","","jpn","oral_presentation","","","","","","","MgAl2O4はCo基ホイスラー合金やCoFe合金などとの格子不整合が1%以下と非常に小さく,また,MgOのような潮解性を持たない上,Mg/Al二層膜やMg-Al(マグナリウム)合金膜のプラズマ酸化を用いて作製可能であるため,MTJのバリア材料として有望である。さらに,MgOと同様にコヒーレントトンネル効果によるTMR増大による巨大TMRが利用可能であり,バリア/強磁性金属界面において高い格子整合性が実現できることから良好なバイアス電圧依存性を示し,高バイアス電圧で用いるデバイス応用にも適している。本研究では,CoFe電極とマグナリウム合金を用いて,より高いTMR比の実現を目指した。また,MgAl-Oxバリアの薄膜化によりトンネル抵抗の低抵抗化を行った。" "Effect of nonmagnetic layer insertion on crystalline barrier magnetic tunnel junction","結晶性障壁強磁性トンネル接合への非磁性層挿入効果","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","第35回 日本磁気学会学術講演会","第35回 日本磁気学会学術講演会","2011-09-27","","jpn","oral_presentation","","","","","","","結晶性強磁性トンネル接合(MTJ)は巨大な磁気抵抗効果だけでなく、多重接合とすることで量子干渉効果の発現が期待される。今回、著者らはこの結晶性MTJにおいて片方の障壁層界面に非磁性金属層を挿入した構造に注目した。この構造は単一障壁MTJでありながら、非磁性層中でスピン依存量子井戸共鳴が起こると理論的に予測されている。Fe/MgO/bcc Cu/Fe(001)接合をスパッタリング法および超高真空蒸着法によって形成し、その磁気伝導特性を評価した。その結果、MgO成膜後にポストアニールを施した試料では磁気抵抗変化率だけでなくコンダクタンスがCu膜厚に対し振動成分を示すことが分かった。これはCu中に形成された量子井戸準位がMgO周りのコヒーレンシーの向上に伴って伝導に反映されたためと考えられる。このようにbcc Cu中の量子井戸準位とMgO障壁周りのコヒーレンシーとの関係を示したのは世界初である。" "Detection of spin-current induced ferromagnetic resonance in nonmagnetic/ferromagnetic junction ","非磁性/強磁性接合におけるスピン流誘起強磁性共鳴の検出","近藤 浩太, 柳原英人, 喜多英治, 介川 裕章, 塚越 一仁, 三谷 誠司, 葛西 伸哉","近藤 浩太, 柳原英人, 喜多英治, 介川 裕章, 塚越 一仁, 三谷 誠司, 葛西 伸哉","2011年日本物理学会秋季大会","2011年日本物理学会秋季大会","2011-09-21","","jpn","oral_presentation","","","","","","","近年、スピンホール効果におけるスピンホール角を定量評価するための手法として、非磁性/強磁性接合系におけるスピン流誘起強磁性共鳴の測定が注目されている。この系では、直流電流を重畳させることで、スピン流による強磁性体のダンピング定数の変調も可能であるため、電流とスピン流の相関を調べるのに適した系である。本講演では強磁性体としてPermalloy、非磁性体としてPtを用いた二層膜における、Ptのスピンホール角とスピン拡散長の評価について報告する。PermalloyおよびPtの膜厚を系統的に変化させる事によって、スピンホール角、スピン拡散長の定量評価が可能となり、それぞれ値は0.036、4.2 nmと評価された。" "Formation of Spin-Dependent Quantum-Well States in Fully Epitaxial Fe/bcc Cu/MgO/Fe(001) Magnetic Tunnel Junctions","フルエピタキシャルFe/bcc Cu/MgO/Fe(001)強磁性トンネル接合におけるスピン依存量子井戸準位の形成 ","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","2011年秋季 第72回 応用物理学会学術講演会","2011年秋季 第72回 応用物理学会学術講演会","2011-08-29","","jpn","oral_presentation","","","","","","","結晶性強磁性トンネル接合(MTJ)は巨大な磁気抵抗効果を発現するため、現在、最も重要なスピントロニクス素子の一つである。今回、著者らはこの結晶性MTJにおいて片方の障壁層界面に非磁性金属層を挿入した構造に注目した。この構造は単一障壁MTJでありながら、まるで二重障壁MTJのように振る舞い、その結果スピン依存量子井戸共鳴が非磁性層中で起こると理論的に予測されている。Fe/MgO/bcc Cu/Fe(001)接合をスパッタリング法および超高真空蒸着法によって形成し、その磁気伝導特性を評価した。その結果、試料の磁気抵抗変化率がCu膜厚に対し振動成分を示すことが分かった。この振動周期を文献にあるCuのバンド分散と比較した結果、Cu中に形成された量子井戸により共鳴トンネルが起こっている可能性が高いことが分かった。単結晶MTJに非磁性層を挿入し、量子井戸層形成を示唆する結果を得たのはこれが世界初である。" "Lattice-matched magnetic tunnel junctions with a MgAl2O4 barrier layer","MgAl2O4スピネル型バリアを用いた格子整合強磁性トンネル接合の開発 ","介川 裕章","介川 裕章","第36回「スピンエレクトロニクス専門研究会」","第36回「スピンエレクトロニクス専門研究会」","2011-08-22","","jpn","oral_presentation","","","","","","","日本磁気学会主催,第36回「スピンエレクトロニクス専門研究会」においてMgAl2O4超薄膜をバリア層とした強磁性トンネル接合についての最近の研究成果を報告する。" "Coherent tunneling effect in a MgAl2O4 spinel based magnetic tunnel junction","Coherent tunneling effect in a MgAl2O4 spinel based magnetic tunnel junction","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","5th International Workshop on Spin Currents","5th International Workshop on Spin Currents","2011-07-25","","jpn","oral_presentation","","","","","","","Recently we developed fully epitaxial MTJs with a normal-spinel-type MgAl2O4(001) barrier. The MgAl2O4 is advantageous because of its nondeliquescence and its small lattice mismatch with typical bcc-CoFe alloys and Co-based Heusler alloys (mismatch ~1%). In the previous report, we showed a large TMR ratio of 117% at room temperature (RT) (165% at 15 K) in an Fe/MgAl2O4/Fe MTJ with an almost perfect lattice matching (~ 1%). The MgAl2O4 layer was prepared using plasma oxidation of a Mg/Al bilayer. However, the oxidation of the Mg/Al bilayer would lead to an inhomogeneous barrier layer. In this study we report an improvement of TMR ratio of MgAl2O4-based MTJs, fabricated using oxidation of a Mg-Al alloy (magnalium) to achieve more homogenous tunnel barrier." "Composition dependence of current-perpendicular-to-plane giant magnetoresistance using Co2FeAl1-xSix Heusler alloys ","Co2FeAl1-xSixホイスラー合金を用いたCPP-GMRの組成依存性","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","5th International Workshop on Spin Currents","5th International Workshop on Spin Currents","2011-07-25","","jpn","oral_presentation","","","","","","","Large MR ratios observed in current-perpendicular giant magnetoresistance (CPP GMR) using thin films of Co2FeAl0.5Si0.5 is also considered to be the evidence of high spin polarization of this alloy. However, CPP GMR using CFAS with other compositions, including Co2FeAl and Co2FeSi, have not been examined yet. Thus, the theoretical prediction is still to be verified experimentally. In this work,CPP-GMR devices with CFAS ferromagnetic layers were systematically investigated by changing the compositions from x=0 to 1 for the purpose of obtaining the most optimized composition for attaining large MR characteristics." "Full Heusler alloy-based spintronic devices","フルホイスラー合金を用いたスピントロニクス素子","三谷 誠司, 介川 裕章, 温 振超, 葛西 伸哉, 猪俣 浩一郎","三谷 誠司, 介川 裕章, 温 振超, 葛西 伸哉, 猪俣 浩一郎","JSPS York-Tohoku Research Symposium","JSPS York-Tohoku Research Symposium","2011-06-27","","jpn","oral_presentation","","","","","","","高スピン分極率を有するホイスラー合金を用いたスピントロニクス素子に関して、NIMSにおける研究開発の成果を紹介する。世界に先駆けてスピン注入磁化反転を実証したこと、新規コヒーレントトンネル材料として有効であるなどを概説する。" "Current-perpedicular-to-plane giant magnetoresistance using Co2FeAl1- x Si x Heusler alloys","Co2FeAl1-xSixホイスラー合金を用いたCPP-GMR","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","IEEE International Conference on Magnetics","IEEE International Conference on Magnetics","2011-04-25","","jpn","oral_presentation","","","","","","","Large MR ratios observed in current-perpendicular giant magnetoresistance (CPP GMR) using thin films of Co2FeAl0.5Si0.5 is also considered to be the evidence of high spin polarization of this alloy. However, CPP GMR using CFAS with other compositions, including Co2FeAl and Co2FeSi, have not been examined yet. Thus, the theoretical prediction is still to be verified experimentally. In this work,CPP-GMR devices with CFAS ferromagnetic layers were systematically investigated by changing the compositions from x=0 to 1 for the purpose of obtaining the most optimized composition for attaining large MR characteristics." "Improvement of tunnel magnetoresistance ratio in fully-epitaxial MgAl2-Ox based magnetic tunnel junctions","Improvement of tunnel magnetoresistance ratio in fully-epitaxial MgAl2-Ox based magnetic tunnel junctions","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","Intermag 2011","Intermag 2011","2011-04-25","","jpn","oral_presentation","","","","","","","Very recently, we reported normal-spinel-type epitaxial barrier MgAl2O4 prepared using plasma oxidation of an Mg/Al bilayer. The MgAl2O4 barrier is advantageous because of its nondeliquescence and its small lattice mismatch with typical bcc-CoFe alloys and Co-based Heusler alloys (~ 1%). We achieved a Fe/MgAl2O4/Fe MTJ with almost perfect lattice matching and few misfit dislocations at the MgAl2O4 barrier interfaces. A large TMR ratio of 117% at room temperature (RT) (165% at 15 K) and a large Vhalf (the bias voltage where the TMR drops to one-half) (-1.3, +1.0 V at RT) were obtained in the lattice matched Fe/MgAl2O4/Fe MTJ. In this study we report an improvement of TMR ratio of MgAl2O4-based MTJs, fabricated using oxidation of Mg-Al alloy (magnalium) instead of the Mg/Al bilayer." "Perpendicular magnetization of Co2FeAl Heusler alloy induced by MgO interface","Co2FeAlホイスラー合金の垂直磁化","温 振超, 介川 裕章, 三谷 誠司, 猪俣 浩一郎","温 振超, 介川 裕章, 三谷 誠司, 猪俣 浩一郎","Intermag 2011","Intermag 2011","2011-04-25","","jpn","oral_presentation","","","","","","","The perpendicular magnetization of Co2FeAl full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density 2x10^6 erg/cm^3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions with high thermal stability at sub-50nm dimension. This work will open up a way for obtaining perpendicular magnetization of Co-based full-Heusler alloys, which is promising for further reduction in the critical current of current induced magnetization switching." "Reflection high-energy electron diffraction study on the formation of crystalline Al-based oxide tunnel barriers on Fe(100)","Fe(100)上における結晶性Al酸化物トンネルバリア形成のRHEED観察","三谷 誠司, 介川 裕章, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","三谷 誠司, 介川 裕章, 新関 智彦, 葛西 伸哉, 猪俣 浩一郎","Intermag 2011","Intermag 2011","2011-04-25","","jpn","oral_presentation","","","","","","","結晶性のMgAl2O4トンネルバリアが大きなトンネル磁気抵抗効果を示すこと最近が見いだされ、そのことに関連して、同じスピネル構造を有する結晶性Al酸化物のバリア形成に関する研究を行った。RHEED観察の結果、Fe(100)表面上では、200度程度の比較的低温の基板加熱により、通常のプラズマ酸化法にて結晶性Al酸化物バリアを成長させることができることが分かった。" "Current-induced magnetization switching in Heusler alloy based devices","ホイスラー合金を用いた磁気抵抗素子におけるスピン注入磁化反転","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","Intermag 2011","Intermag 2011","2011-04-25","","jpn","oral_presentation","","","","","","","MRAM等スピントロニクス素子の動作において、スピン注入磁化反転は必要不可欠な現象・技術である。スピン分極率が大きく、磁化のダンピング定数の小さいホイスラー合金は高効率スピン注入磁化反転が期待されており、それを世界にさきがけて行った結果を関連データとともにレビューする。" "Formation of Spin Dependent Quantum Well States in Fully Epitaxial Fe/bcc Cu/MgO/Fe(001) Junctions","フルエピタキシャルFe/bcc Cu/MgO/Fe(001)強磁性トンネル接合におけるスピン依存量子井戸の形成","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","2011年春季 第58回 応用物理学関係連合講演会","2011年春季 第58回 応用物理学関係連合講演会","2011-03-24","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)の障壁層を二枚にした2重強磁性トンネル接合(DMTJs)は、将来的にスピントランジスタの実現につながるため重要である。今回、著者らは単一MTJにおいて片方の障壁層界面に非磁性金属層を挿入した擬DMTJs構造に注目した。この構造はDMTJsよりも作製が容易でありながら、DMTJsと同様にスピン依存量子井戸共鳴が起こるという理論予測がある。Fe/bcc Cu/MgO/Fe(001)接合をマグネトロンスパッタリング法および超高真空蒸着法によって形成し、その磁気伝導特性を評価した。その結果、磁気抵抗変化率がCu膜厚に対し振動成分を伴って減衰することが分かった。文献にあるCuのバンド分散との比較から、この振動はCu中に形成された量子井戸に起因する可能性が高いことが分かった。単結晶MTJに非磁性層を挿入し、量子井戸層形成を示唆する結果を得たのはこれが世界初である。" "Composition dependence of CPP-GMR using Co2FeAl1-xSix Heusler alloys","Co2FeAl1-xSixホイスラー合金を用いたCPP-GMRの組成依存性","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","2011年春季 第58回 応用物理学関係連合講演会","2011年春季 第58回 応用物理学関係連合講演会","2011-03-24","","jpn","oral_presentation","","","","","",""," L21構造のCo2FeAl1-xSix (CFAS)ホイスラー合金のバンド計算によれば,x=0.5の時にフェルミ準位がギャップの中心に位置し,熱擾乱や規則構造の乱れに対して強いハーフメタルとなると考えられ,PCARによるスピン分極率測定の結果もこれを支持している. CPP-GMRについてもx=0.5の組成についてAgスペーサーを用いた素子で比較的高いMR比が確認されているが,組成xに対するMRの依存性は調べられていない.x=0.5 のCFAS薄膜は,高いMR比が得られるような熱処理条件の下ではB2構造であるが,これに対し Co2FeSi (CFS)薄膜ではよりL21構造が得られやすい[3].従って,CFASのSiの割合xを増やすとL21構造がより出来やすくなると考えられ,バンド構造に加え結晶規則度も考慮に入れると,x>0.5に大きなMRを得るための最適な組成がある可能性がある.本研究ではAlとSiの組成比を変えたCFAS薄膜を用いてCPP-GMR素子を作成し,構造とMR特性に及ぼす組成の効果を調べた." "Large tunnel magnetoresistance in magnetic tunnel junctions with an epitaxial Mg-Al-Ox barrier","エピタキシャルMg-Al-Oxバリア層を用いた強磁性トンネル接合における大きなトンネル磁気抵抗","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","2011年春季 第58回 応用物理学関係連合講演会","2011年春季 第58回 応用物理学関係連合講演会","2011-03-24","","jpn","oral_presentation","","","","","","","MgAl2O4は正スピネル構造を持つ絶縁体材料であり,CoFe合金やCo基ホイスラー合金などと格子不整合が1%以下と小さく, また,MgOのような潮解性を持たないため,強磁性トンネル接合(MTJ)の新規バリア材料として有望である。特に,MgとAl組成を変えることによって,バリア層の格子定数を調整できる可能性があるため,バリア界面にミスフィット欠陥が存在しない理想的なMTJ実現につながると期待される。我々は,Mg/Al積層膜のプラズマ酸化によって作製したエピタキシャルMgAl2O4バリアを実現し,その良好なトンネル磁気抵抗(TMR)特性を報告した。本研究では,より高品質なMgAl2O4バリア作製のために,Mg-Al(マグナリウム)合金を用い,より高いTMR比を目指した。また,MgAl2O4バリアのトンネル抵抗低減の可能性についても検討した。" "Epitaxial tunnel junctions with a Mg-Al-Ox layer","Mg-Al酸化物を用いたエピタキシャル強磁性トンネル接合","介川 裕章","介川 裕章","文部科学省科学研究費補助金 特定領域研究「スピン流の創出と制御」","文部科学省科学研究費補助金 特定領域研究「スピン流の創出と制御」","2011-02-23","","jpn","oral_presentation","","","","","","","強磁性トンネル接合用の新規バリア材料であるMg-AlOxバリアの作製法について検討し,熱処理条件の最適化により大きなトンネル磁気抵抗効果が得られることを示す。また,この材料の現状や将来性,デバイスへの応用性のメリット等を講演する。" "Magnetic tunnel junctions with MgAl2O4 spinel barrier layer","MgAl2O4スピネルバリア層を用いた強磁性トンネル素子の開発","介川 裕章","介川 裕章","IDEMAヘッド・ディスク部会","IDEMAヘッド・ディスク部会","2011-02-18","","jpn","oral_presentation","","","","","","","HDDや不揮発メモリMRAMへ応用可能な新規スピネル型MgAl2O4バリア材料の作製法や,応用上の有効性について講演する。" "Epitaxial magnetic tunnel junctions with a MgAl2O4(001) barrier","Epitaxial magnetic tunnel junctions with a MgAl2O4(001) barrier","介川 裕章, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 三谷 誠司, 猪俣 浩一郎","Workshop on Heusler Alloys and Their Spintronics Applications","Workshop on Heusler Alloys and Their Spintronics Applications","2011-01-26","","jpn","oral_presentation","","","","","","","MgAl2O4バリアは,bcc型のFeやホイスラー合金との格子マッチングが極めて良好であり,非潮解性であることから,新規強磁性トンネル接合用トンネルバリアに有効である。本発表ではこのMgAl2O4バリアについて講演する。またホイスラー合金を用いたスピン注入磁化反転についても報告する。" "Improvement of bias voltage dependence in lattice-matched MgAl2O4-based magnetic tunnel junctions","Improvement of bias voltage dependence in lattice-matched MgAl2O4-based magnetic tunnel junctions","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","ICAUMS2010 (International Conference of AUMS)","ICAUMS2010 (International Conference of AUMS)","2010-12-05","","jpn","oral_presentation","","","","","","","MgO-based magnetic tunnel junctions (MTJs) with large tunnel magnetoresistance (TMR) ratio are now commonly used in spintronics devices such as magnetoresistive random access memories (MRAMs) and read head sensors of hard disc drives. The TMR enhancement in MgO-based MTJs originates from the coherent tunnelling through a crystalline MgO tunnel barrier with a high (001) orientation. However the TMR ratio greatly decreases with a bias voltage application. This problem possibly relates to defects at interfaces of a barrier and deterioration of its crystallinity due to the large lattice mismatch between MgO and bcc-FeCo based ferromagnetic layers. In order to improve the bias voltage dependence of TMR, effect of the lattice matching using other crystalline barriers should be examined. In this " "Bias voltage dependence of tunnel magnetoresistance for fully-epitaxial Fe/spinel MgAl2O4/Fe junctions","Bias voltage dependence of tunnel magnetoresistance for fully-epitaxial Fe/spinel MgAl2O4/Fe junctions","介川 裕章, シュウ フイシン, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","MMM2010 55th Annual Conference on Magnetism and Magnetic Materia","MMM2010 55th Annual Conference on Magnetism and Magnetic Materia","2010-11-14","","jpn","oral_presentation","","","","","","","Recent progress of crystalline MgO-based magnetic tunnel junctions (MTJs) has accelerated the applications for spintronics devices such as magnetoresistive random access memories and read heads in hard disk drives. However tunnel magnetoresistance (TMR) generally drops with a bias voltage application, which presumably relates to defects at interfaces of a barrier. Further improvement of the bias voltage dependence of TMR is required for wider application of MTJs. In this study we have newly explored normal-spinel-type epitaxial barrier MgAl2O4 using plasma oxidation of an Mg/Al bilayer. The MgAl2O4 barrier is advantageous because of its nondeliquescence and its small lattice mismatch with typical bcc CoFe alloys and Heusler alloys. Therefore MgAl2O4-based MTJs should have almost perfect l" "Fabrication of epitaxial Fe/MgAl2O4/Fe ferromagnetic tunnel junctions","エピタキシャルFe/MgAl2O4スピネル/Fe強磁性トンネル接合の作製","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","日本金属学会2010年秋期(第147回)大会","日本金属学会2010年秋期(第147回)大会","2010-09-25","","jpn","oral_presentation","","","","","","","強磁性トンネル接合(MTJ)のバリア層には,巨大トンネル磁気抵抗(TMR)が得られる結晶質のMgOが主に用いられている。我々は最近,結晶質の新しいバリア材料として,MgAl2O4(スピネル)が作製可能なことを示した。本研究ではより高品質なMgAl2O4バリアの作製方法を検討し,Fe/MgAl2O4/Fe構造を有するフルエピタキシャルMTJ構造を通して,それらの特徴を調べた。" "Lattice-matched magnetic tunnel junctions with epitaxial MgAl2O4 barrier -An improved preparation method using a magnalium alloy","スピネルMgAl2O4バリアを用いた格子整合強磁性トンネル接合〜マグナリウム(Mg-Al合金)層による作製方法","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","2010年秋季 第71回 応用物理学会学術講演会","2010年秋季 第71回 応用物理学会学術講演会","2010-09-14","","jpn","oral_presentation","","","","","","","MgAl2O4はCoFe合金やCo基ホイスラー合金などと格子不整合が1%以下と非常に小さく,また,MgOのような潮解性を持たないため,強磁性トンネル接合(MTJ)などの新規バリア材料として有望である。我々は,エピタキシャルMgAl2O4バリアを用いたFe/MgAl2O4/Fe構造のMTJによって,室温で117%,低温で165%のトンネル磁気抵抗(TMR)比を実現した。さらに,TMR比のバイアス電圧依存性が非常に小さいという特長があることを示した。これは,FeとMgAl2O4との格子整合性が極めて良いためであると考えられる。しかし,MgAl2O4層はMg/Al積層膜をプラズマ酸化により作製しているため,バリア内にMgとAlの濃度分布がある。本研究ではより均質で高品質なMgAl2O4層の作製を目指し,AlとMgの合金であるマグナリウム膜を酸化することによってFe/MgAl2O4/Fe構造を作製した。" "Fully epitaxial Fe/MgO/Fe(001) junctions with nonmagnetic layer insersion","フルエピタキシャルFe/MgO/Fe(001)接合界面への非磁性層挿入","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","新関 智彦, 三谷 誠司, 介川 裕章, 葛西 伸哉, 猪俣 浩一郎","2010年秋季 第71回 応用物理学会学術講演会","2010年秋季 第71回 応用物理学会学術講演会","2010-09-14","","jpn","oral_presentation","","","","","","","スピン依存共鳴トンネル効果の実現を狙いFe/MgO/Feトンネル接合に非磁性層を挿入した構造を作製した。非磁性体中のデルタ1対称性を有する電子の量子井戸準位形成の可能性のあるAg層を用いて、初めてスピンに依存した伝導(磁気抵抗効果)を室温で観測した。スピン依存共鳴トンネル効果を用いた高集積度MRAMの開発に向けた第一歩となる成果である。" "CPP-GMR devices using Co2FeAl1-xSix Heusler alloys: composition dependence of MR","Co2FeAl1-xSixホイスラー合金を用いたCPP-GMR素子における MRの組成依存性","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","第34回日本磁気学会学術講演会","第34回日本磁気学会学術講演会","2010-09-04","","jpn","oral_presentation","","","","","",""," 高いスピン分極率を持つハーフメタルはCPP-GMR素子の高MR比のために有用であると期待される. L21構造のCo2FeAl1-xSix (CFAS)ホイスラー合金はバンド計算によればx=0.5の時にフェルミ準位がギャップの中心に位置し、熱擾乱や規則構造の乱れに対して強いハーフメタルとなると考えられている。実際CPP-GMRについてもx=0.5の組成について比較的高いMR比が実験的に確認されているが、MRの組成xに対する依存性は実験的には調べられていない。Co2FeAl (CFA)とCo2FeSi (CFS)を比較すると、薄膜においてCFSの方がよりL21構造が得られやすい。従って、CFASのSiの割合xを増やすとL21構造がより出来やすくなると考えられ、バンド構造に加え結晶規則度も考慮に入れると、x>0.5に最適な組成がある可能性がある。本研究ではこのような観点から最適な組成を探る目的で、CFAS薄膜を用いてCPP-GMR素子を作成し、構造とMR特性に及ぼす組成の効果を調べた。" "Spin-dependent scattering in the CPP-GMR with Co2FeAl0.5Si0.5 Heusler alloy","Co2FeAl0.5Si0.5ホイスラー合金CPP-GMRのスピン依存散乱","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","第34回日本磁気学会学術講演会","第34回日本磁気学会学術講演会","2010-09-04","","jpn","oral_presentation","","","","","","","ホイスラー合金Co2FeAl0.5Si0.5を強磁性体に,Agをスペーサーに用いたCPP-GMR素子におけるスピン依存散乱,特に界面散乱を定量的に評価した." "Magnetic tunnel junctions with epitaxial MgAl2O4 or gamma-Al2O3 barrier","エピタキシャルMgAl2O4およびγ-Al2O3バリア層を有する強磁性トンネル接合","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 大久保 忠勝, 新関 智彦, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","第34回日本磁気学会学術講演会","第34回日本磁気学会学術講演会","2010-09-04","","jpn","oral_presentation","","","","","","","MRAMや磁気ヘッドセンサに用いられる強磁性トンネル接合(MTJ)のトンネルバリア材料として,巨大トンネル磁気抵抗比(TMR比)が実現可能な結晶質MgOが主として用いられている。MgO単一層の他にも結晶質バリア材料としてMgO/ZnO複合構造が報告されている。我々は最近,Mg/Al積層膜をプラズマ酸化することにより,エピタキシャル成長したスピネル型MgAl2O4(スピネル)バリアが成長することを見出した。MgAl2O4はCo基ホイスラー合金やFeなどと格子不整合が1%以下と非常に小さく,また,MgOのような潮解性を持たないため,MTJの新規バリア材料として有望である。本研究では,Fe(001)上にMgAl2O4 3)およびスピネル類似構造を持つγ-Al2O3の作製方法を確立し,Fe/バリア/Fe構造を有するフルエピタキシャルMTJ構造を通して,それらの特徴を調べた。" "CPP spin-valves using heat-resistant NiAl layers","NiAl耐熱層を用いたCPPスピンバルブ","長谷 直基, 中谷 友也, ボラプラガダ バラプラサド, 古林 孝夫, 介川 裕章, 葛西 伸哉, 高橋 有紀子, 宝野 和博","長谷 直基, 中谷 友也, ボラプラガダ バラプラサド, 古林 孝夫, 介川 裕章, 葛西 伸哉, 高橋 有紀子, 宝野 和博","International Symposium on Advanced Magnetic Materials and Appli","International Symposium on Advanced Magnetic Materials and Appli","2010-07-12","","jpn","oral_presentation","","","","","","","The employment of half metallic Heusler alloys as ferromagnetic electrodes is a promising way to obtain the low device resistance and the high magnetoresitive output in current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. It is well-known that the heat treatment to the Heusler layer is indispensable to obtain the ordered crystal structures such as the B2 or the L21 structure with which higher half metallicity is expected [1]. Sakuraba et al. reported that the interdiffusion due to the heat treatment among the Heusler and other layers makes the degree of B2, L21 ordering and the MR output degrade [2]. Hence, it is important to suppress the interdiffusion around the Heusler layers to extract a higher performance from Heusler alloy layers. In this work, we have studied th" "Bulk scattering contribution to CPP-GMR of Co2FeAl0.5Si0.5/Ag/Co2FeAl0.5Si0.5 trilayer","Co2FeAl0.5Si0.5/Ag/Co2FeAl0.5Si0.5におけるCPP-GMRのバルク散乱の効果","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","ISAMMA2010","ISAMMA2010","2010-07-12","","jpn","oral_presentation","","","","","","","Co2FeAl0.5Si0.5ホイスラー合金とAgを用いたCPP-GMR素子におけるバルクスピン散乱を定量的に報告する." "Magnetic tunnel junctions with a spinel MgAl2O4 barrier","Magnetic tunnel junctions with a spinel MgAl2O4 barrier","介川 裕章, シュウ フイシン, 古林 孝夫, 新関 智彦, Wenhong Wang, 葛西 伸哉, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 古林 孝夫, 新関 智彦, Wenhong Wang, 葛西 伸哉, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","ISAMMA2010","ISAMMA2010","2010-07-12","","jpn","oral_presentation","","","","","","","MgO-based magnetic tunnel junctions (MTJs) are now commonly used in spintronics devices such as magnetoresistive random access memories (MRAMs) due to their high tunnel magnetoreisitance (TMR) ratio. Spin dependent tunneling through a crystalline barrier is an important issue in spintronics. Very recently we prepared epitaxial MgAl2O4 spinel type tunnel barrier prepared on a half-metallic Heusler alloy Co2FeAl0.5Si0.5 using sputter deposition and plasma oxidation . The lattice of MgAl2O4 matches well with typical bcc ferromagnetic electrodes such as Fe, CoFe and Co-based Heusler alloys. However detailed spin-dependent transport properties of MTJs using an MgAl2O4 barrier have not been characterized yet. In this study we examined the structure and TMR properties of Fe/MgAl2O4/Fe MTJs." "CPP-GMR devices with epitaxial layers of Heusler alloys","ホイスラー合金エピタキシャル膜を用いたCPP-GMR素子","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 中谷 友也, ハリ ゴリパティ, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","日本金属学会2010年春期大会","日本金属学会2010年春期大会","2010-03-28","","jpn","oral_presentation","","","","","",""," CPP-GMR素子は高密度ハードディスク用読み取りMRヘッドとして有望であるが、現状では十分なMR比が得られておらず、低い電気抵抗を保ちながら高MR比を実現することが求められている。ハーフメタルとなるホイスラー合金をCPP-GMRに適用することにより高いMR比が実現されるものと期待される。本研究ではトンネル接合において高いMR比が得られており、高いスピン分極率を持つものと考えられるホイスラー合金、Co2FeAl0.5Si0.5 (CFAS)及びCo2MnSi(CMS)を強磁性層として用い、Agのスペーサー層と組み合わせたエピタキシャル多層構造からなるスピンバルブ型及び擬スピンバルブ型のCPP-GMR素子を作製し、そのMR特性を調べた。" "CPP-GMR with Co2FeAl0.5Si0.5 Heusler alloy","Co2FeAl0.5Si0.5ホイスラー合金を用いたCPP-GMR素子","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","日本金属学会2010年春期(第146回)大会講演","日本金属学会2010年春期(第146回)大会講演","2010-03-28","","jpn","oral_presentation","","","","","","","磁気センサーへの応用から近年活発に研究されている,ホイスラー合金ベースのCPP-GMR素子について,そのスピン依存散乱と非磁性スペーサー材料の選択について発表する." "CPP-GMR devices with Co2FeAl0.5Si0.5 Heusler alloys","Co2FeAl0.5Si0.5 ホイスラー合金を用いた CPP-GMR 素子","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 三谷 誠司, 宝野 和博","2010年春季 第57回応用物理学関係連合講演会","2010年春季 第57回応用物理学関係連合講演会","2010-03-17","","jpn","oral_presentation","","","","","","","ホイスラー合金Co2FeAl0.5Si0.5を用いたCPP-GMRにおけるスピン依存散乱について詳細に解析した." "Tunnel Magnetoresistance in fully epitaxial Fe/MgAl2O4/Fe magnetic tunnel junctions","フルエピタキシャルFe/MgAl2O4/Fe強磁性トンネル接合のTMR効果","介川 裕章, シュウ フイシン, 新関 智彦, 王 文洪, 葛西 伸哉, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シュウ フイシン, 新関 智彦, 王 文洪, 葛西 伸哉, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","第57回応用物理学会関係連合講演会","第57回応用物理学会関係連合講演会","2010-03-17","","jpn","oral_presentation","","","","","","","MRAM や磁気ヘッドセンサに用いられる強磁性トンネル接合(MTJ)のトンネルバリア材料として,巨大トンネル磁気抵抗比(TMR 比)が実現できる結晶質MgO が主として用いられている。MgO 以外の結晶質バリア材料の研究としてZnSe等があるが,結晶質に起因する特徴的な効果等は実験的に得られていなかった。本研究では新規材料としてMgAl2O4 を用いたMTJ作製法を検討した。特にFe/MgAl2O4/Fe 構造の作製条件を検討するとともに,構造及びTMR効果を詳細に調べた。" "A large tunnel magnetoresistance at room temperature in epitaxial Co2FeAl/MgO/CoFe magnetic tunnel junctions ","A large tunnel magnetoresistance at room temperature in epitaxial Co2FeAl/MgO/CoFe magnetic tunnel junctions ","王 文洪, 介川 裕章, 三谷 誠司, 猪俣 浩一郎","王 文洪, 介川 裕章, 三谷 誠司, 猪俣 浩一郎","THE 11TH JOINT MMM–INTERMAG CONFERENCE","THE 11TH JOINT MMM–INTERMAG CONFERENCE","2010-01-18","","jpn","oral_presentation","","","","","","","The search for new ferromagnetic materials that show giant tunneling magnetoresistance (TMR) effect at room temperature (RT) in MgO-based magnetic tunnel junctions (MTJs) is currently one of most topic field in spintronics. Here we provide a new Heusler alloy of Co2FeAl (CFA), which exhibits giant TMR ratio of 330% at RT in CFA/MgO/CoFe MTJ fabricated using simple sputter-deposition techniques for all the layers. We found that the TMR exhibits oscillatory behavior as a function of thickness of MgO barrier with the period of 0.33 nm. CFA has the lowest damping constant in Heusler alloys, which is important in spin dynamics [1]. Thus, our finding suggests that the junction using CFA may play a key role in future spintronics devices operating at RT." "Spin-transfer magnetization switching in full-Heusler Co2FeAl0.5Si0.5/Ag/Co2FeAl0.5Si0.5 epitaxial nanopillars","Spin-transfer magnetization switching in full-Heusler Co2FeAl0.5Si0.5/Ag/Co2FeAl0.5Si0.5 epitaxial nanopillars","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","11th Joint MMM-Intermag Conreference","11th Joint MMM-Intermag Conreference","2010-01-18","","jpn","oral_presentation","","","","","","","We report magnetization switching by spin-transfer torque in an epitaxial spin-valve nanopillar made with a half-metallic full-Heusler Co2FeAl0.5Si0.5 (CFAS) alloy. The CFAS/Ag/CFAS spin valves showed a magnetoresistance ratio of 7–9%, and spin-transfer switching was clearly observed in the nanopillar by applying a relatively small dc current (~10^6 A/cm2 in current density). Statistical analysis based on a thermal activation model revealed an averaged critical current density (Jc0) of 9.3x10^6 A/cm2 with a thermal stability factor (KV/kBT) of ~40." "CPP spin valve with all B2 Co2FeAl0.6Si0.4/NiAl/Co2FeAl0.6Si0.4 trilayer","Co2FeAl0.6Si0.4/NiAl/Co2FeAl0.6Si0.4オールB2規則3層膜を用いたCPPスピンバルブ","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 宝野 和博","中谷 友也, 古林 孝夫, 葛西 伸哉, 介川 裕章, 高橋 有紀子, 宝野 和博","11th Joint MMM-Intermag Conference 2010 ","11th Joint MMM-Intermag Conference 2010 ","2010-01-18","","jpn","oral_presentation","","","","","","","We report a new spacer layer material NiAl for current perpendicular to plane giant magnetoresistace devices with Heusler ferromagnetic alloys." "高スピン偏極材料を用いたスピントロニクスデバイスのナノ構造解析 ","高スピン偏極材料を用いたスピントロニクスデバイスのナノ構造解析 ","高橋 有紀子, 中谷 友也, 古林 孝夫, 介川 裕章, 猪俣 浩一郎, 宝野 和博","高橋 有紀子, 中谷 友也, 古林 孝夫, 介川 裕章, 猪俣 浩一郎, 宝野 和博","2009年度 スピン流の創出と制御 成果報告会","2009年度 スピン流の創出と制御 成果報告会","2010-01-13","","jpn","oral_presentation","","","","","","","TMR素子やCPP-GMR素子のMR比は電流のスピン偏極率に依存するので絶縁相や非磁性相をはさむ上下電極にスピン偏極率が100%のハーフメタルを用いるとMR比を増加させることができる。加えて、MR比を増加させるためには理想的な界面を実現する必要がある。しかし、多くの研究では素子製造プロセスを変化させることにより特性を最適化することに多くの努力がなされ、MR素子の構造を詳細に解析してMR特性を構造的な観点から議論した研究が少ない。そこで本研究では電極として用いられる高スピン偏極材料および素子の物性と素子構造を詳細に解析し、TMR素子やCPP-GMR素子で高いMR特性を得るための材料設計指針を提案することを目的としている。" "Tunnel magnetoresistance in magnetic tunnel junctions with spinel MgAl2Ox barrier","スピネル型MgAl2Oxバリアを有する強磁性トンネル接合のTMR効果","介川 裕章","介川 裕章","第28回「スピンエレクトロニクス専門研究会」","第28回「スピンエレクトロニクス専門研究会」","2010-01-12","","jpn","oral_presentation","","","","","","","MRAMや磁気ヘッドセンサに用いられる強磁性トンネル接合(MTJ)のトンネルバリア材料として,巨大トンネル磁気抵抗比(TMR比)が実現できる結晶質MgOが主として用いられている。我々は最近,Mg/Al積層膜をプラズマ酸化することにより,ホイスラー合金Co2FeAl0.5Si0.5(001)層上にエピタキシャル成長したスピネル型MgAl2O4(001)(スピネル)バリアが成長することを見出した。MgAl2O4はCo基ホイスラー合金やFeなどと格子不整合が1%以下と非常に小さく,また,MgOのような潮解性を持たない。本研究ではFe/MgAl2O4/Fe構造の作製条件を検討するとともに、構造及びTMR効果を詳細に調べた。" "CPP-GMR using NiAl B2 intermetallic compound for the spacer layer","NiAl B2金属間化合物をスペーサ層に用いたCPP-GMR素子","中谷 友也, 古林 孝夫, 介川 裕章, 高橋 有紀子, 宝野 和博","中谷 友也, 古林 孝夫, 介川 裕章, 高橋 有紀子, 宝野 和博","日本金属学会2009年秋期大会","日本金属学会2009年秋期大会","2009-09-15","","jpn","oral_presentation","","","","","","","スペーサ層としてNiAl金属間化合物を用いたCPP-GMR三層膜における,層間交換結合および磁気抵抗特性を発表する." "Transport properties of CPP-GMR spin valve device using Co2MnGa0.5Sn0.5 Heusler alloy","Co2MnGa0.5Sn0.5ホイスラー合金を用いたCPP-GMRスピンバルブ","長谷 直基, 中谷 友也, ボラプラガダ バラプラサド, 高橋 有紀子, 古林 孝夫, 介川 裕章, 宝野 和博","長谷 直基, 中谷 友也, ボラプラガダ バラプラサド, 高橋 有紀子, 古林 孝夫, 介川 裕章, 宝野 和博","日本金属学会2009年秋期大会","日本金属学会2009年秋期大会","2009-09-15","","jpn","oral_presentation","","","","","","","Co基ホイスラー合金(Co2FeAl0.5Si0.5やCo2MnSi)は、そのハーフメタル性から高スピン偏極源として期待される材料である。我々は最近、Co2MnGa0.5Sn0.5(CMGS)合金が単相のホイスラー型金属間化合物を形成し、PCAR法を用いて4.2Kで72%の高いスピン分極率を示すことを報告した。本研究では、このホイスラー合金を強磁性電極としたスピンバルブ型CPP-GMR素子を試作し、そのMR特性を評価することによりCo2MnGa0.5Sn0.5合金の新たなスピン偏極源としての可能性を検討した。" "Magnetic tunnel junctions with Heusler alloy Co2FeAl0.5Si0.5 electroles and spinel MgAl2O4 barrier","ホイスラー合金Co2FeAl0.5Si0.5とスピネルMgAl2O4トンネルバリア用いたエピタキシャル強磁性トンネル接合","シャン ロン, 介川 裕章, 王 文洪, 小塚 雅也, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","シャン ロン, 介川 裕章, 王 文洪, 小塚 雅也, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","2009年秋期(145回)日本金属学会講演会","2009年秋期(145回)日本金属学会講演会","2009-09-15","","jpn","oral_presentation","","","","","","","高キュリー点をもつCo2FeAl0.5Si0.5 (CFAS)フルホイスラー合金はバンド計算からハーフメタルとして期待されており,盛んに研究がなされている。本研究では,MgO単結晶基板上に成膜したCFAS/MgAlOxバリア/CoFeエピタキシャル強磁性トンネル接合(MTJ)を作製し,CFAS層のハーフメタル特性について報告する。" "Giant magnetoresistance in a magnetic tunnel junction with full-Heusler Co2FeAl alloys","フルホイスラー合金Co2FeAl層を有する強磁性トンネル接合の巨大TMR","王 文洪, 介川 裕章, 猪俣 浩一郎, M. Wojcik, シャン ロン, 三谷 誠司","王 文洪, 介川 裕章, 猪俣 浩一郎, M. Wojcik, シャン ロン, 三谷 誠司","2009年秋期(145回)日本金属学会講演会","2009年秋期(145回)日本金属学会講演会","2009-09-15","","jpn","oral_presentation","","","","","","","我々は高スピン分極材料,Co2FeAl0.5Si0.5 (CFAS)フルホイスラー合金のハーフメタル特性について報告してきた。ごく最近MBEで作製されたCFAS/MgO/CFAS MTJにおいて室温で386%のTMR比が報告され,CFAS層のハーフメタル性と良好な温度特性が実証された。本論では,ハーフメタルではないためこれまであまり注目されてこなかったCo2FeAl (CFA)ホイスラー合金を用いてフルエピタキシャルMTJ構造を作製し,巨大TMRを実現したので報告する。" "Tunnel magnetoresistance and microstructure of a Co2FeAl0.5Si0.5/MgAl2O4/CoFe tunnel junction","Co2FeAl0.5Si0.5/MgAl2O4/CoFe強磁性トンネル接合のトンネル磁気抵抗効果と微細構造","介川 裕章, シャン ロン, 王 文洪, 小塚 雅也, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, シャン ロン, 王 文洪, 小塚 雅也, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","第33回日本磁気学会学術講演会","第33回日本磁気学会学術講演会","2009-09-12","","jpn","oral_presentation","","","","","","","フルホイスラー合金Co2FeAl0.5Si0.5(CFAS)はハーフメタルと理論予測されており,実験的にもCFAS/MgO/CFAS構造の強磁性トンネル接合(MTJ)において巨大なTMRが報告されている。この材料の特徴は,CFASのマイノリティスピンバンドギャップのほぼ中央にフェルミ準位が位置することであり,B2構造でもハーフメタル特性を保ち,良好な温度特性が期待されている。本研究では,CFAS層のPを実験的に決定し,同時に,スピン依存トンネル分光によりCFAS層の電子構造についての情報を得るため,AlOxバリアとCoFe上部電極を有するMTJを作製し,伝導特性および微細構造の評価を行った。" "Transport properties of CPP-GMR spin valve device using Co2MnGa0.5Sn0.5 Heusler alloy","Co2MnGa0.5Sn0.5ホイスラー合金を用いたCPP-GMRスピンバルブ","長谷 直基, 中谷 友也, ボラプラガダ バラプラサド, 高橋 有紀子, 古林 孝夫, 介川 裕章, 宝野 和博","長谷 直基, 中谷 友也, ボラプラガダ バラプラサド, 高橋 有紀子, 古林 孝夫, 介川 裕章, 宝野 和博","第33回日本磁気学会学術講演会","第33回日本磁気学会学術講演会","2009-09-12","","jpn","oral_presentation","","","","","","","CPP(Current-perpendicular-to-plane)-GMR素子は、素子を構成する全ての層が金属から成るために、絶縁体層を用いるtunneling magnetoresistance(TMR)素子に比べて素子抵抗を低くでき、高速応答が必要とされる次世代の高密度磁気記録用再生ヘッド等への応用の可能性がある。我々は最近Co2MnGa0.5Sn0.5(CMGS)合金が単相のホイスラー型金属間化合物を形成し、PCAR(Point Contact Andreev Reflection)法を用いて4.2Kで少なくとも72%のスピン分極率を示すことを報告した。本研究では、このホイスラー合金を強磁性電極としたスピンバルブ型CPP-GMR素子を試作し、そのMR特性を評価することによりCo2MnGa0.5Sn0.5合金の新たなスピン分極源としての可能性を検討した。実験結果としては、CMGSMホイスラー合金を用いたCPP-GMR素子でMR比が4.5%、面積×抵抗値、RA=88.8 mΩμm2、抵抗変化量⊿RA=3.81 mΩμm2を得た。今後種々の条件の最適化、特にCMGS層の組成の最適化を" "Spin-transfer switching in Co2FeAl0.5Si0.5/Ag/Co2FeAl0.5Si0.5 CPP-GMR","Co2FeAl0.5Si0.5/Ag/Co2FeAl0.5Si0.5構造を有するCPP-GMR素子のスピン注入磁化反転","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","第33回日本磁気学会学術講演会","第33回日本磁気学会学術講演会","2009-09-12","","jpn","oral_presentation","","","","","","","スピン注入磁化反転はMRAMなど,スピントロニクスデバイスの情報書き込み技術として注目されている。Slonczewskiのモデルによれば,スピン注入効率gは強磁性層のスピン分極率向上にしたがって増大するため,高スピン偏極材料を強磁性層として用いれば反転電流密度Jcの低減が期待される。近年,フルホイスラーCo2FeAl0.5Si0.5(CFAS)合金を用いたMTJやCPP-GMR素子において室温で高いMR比が報告されるようになった。本研究では,高スピン偏極材料としてこのCFAS合金に着目し,CPP-GMR素子におけるスピン注入磁化反転について研究を行った。" "Effects of spin accumulation in ferromagnetic double tunnel junctions I","強磁性2重トンネル接合におけるスピン蓄積効果I","三谷 誠司, 介川 裕章, 葛西 伸哉","三谷 誠司, 介川 裕章, 葛西 伸哉","日本磁気学会学術講演会","日本磁気学会学術講演会","2009-09-12","","jpn","oral_presentation","","","","","","","2重トンネル接合は、スピン蓄積による大きな化学ポテンシャルの分裂を実現できるナノ構造であり、その理解や機能応用に興味が持たれる。本研究では、強磁性2重トンネル接合におけるスピン蓄積の効果を調べるために、第一段階として、(i)簡単なモデルによる、スピン蓄積がTMRに及ぼす効果の計算、および、(ii)その実験的観測のための試料作製条件の検討を行った。" "CPP-GMR using Co2Fe(Al,Si) Heusler alloy and NiAl spacer layer","Co2Fe(Al,Si)ホイスラー合金とNiAlスペーサを用いたCPP-GMR","中谷 友也, 古林 孝夫, 介川 裕章, 高橋 有紀子, 宝野 和博","中谷 友也, 古林 孝夫, 介川 裕章, 高橋 有紀子, 宝野 和博","第33回日本磁気学会学術講演会","第33回日本磁気学会学術講演会","2009-09-12","","jpn","oral_presentation","","","","","","","Co2Fe(Al,Si)ホイスラー合金に対し,NiAlをスペーサ層に用いたCPP-GMR素子の磁気抵抗特性を発表する." "CPP-GMR in spin valves using epitaxial layers of Heusler alloys and Ag spacer","エピタキシャルホイスラー合金層と Agスペーサ層を用いたスピンバルブのCPP-GMR","古林 孝夫, 小玉 恒太, 中谷 友也, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 小玉 恒太, 中谷 友也, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","第33回日本磁気学会学術講演会","第33回日本磁気学会学術講演会","2009-09-12","","jpn","oral_presentation","","","","","",""," トンネル接合において高いMR比が得られているホイスラー合金、Co2FeAl0.5Si0.5 (CFAS)及びCo2MnSi(CMS)を強磁性電極としてAgをスペーサ層に用いたCPP-GMR素子を作製し、そのMR特性を調べた。 CFASを用いたCPP-GMR素子の積層構造は下からCr(10)/Ag(200)/CFAS(20)/Ag(5)/CFAS(5)/CoFe(2)/IrMn(10)/Ru(8)(数字は厚さ、nm)であり、下部及び上部CFAS層をスパッタした後、それぞれ400˚Cでのアニールを行った。断面TEM観察により上部CFAS層までのエピタキシャル成長が確認された。室温でMR比12.4%、面積×抵抗値、RA =0.121 Ω(μm)2、抵抗変化量 ΔRA =15 mΩ(μm)2が得られた。CMSを用いたCPP-GMR素子においては、11.8%のMR比が得られた。" "Giant tunnel magnetoresistance in full-Heusler alloy Co2FeAl-based magnetic tunnel junctions","フルホイスラー合金Co2FeAl/MgO/CoFe強磁性トンネル接合における巨大TMR比","王 文洪, 介川 裕章, 猪俣 浩一郎","王 文洪, 介川 裕章, 猪俣 浩一郎","2009年秋季 第70回 応用物理学会 学術講演会","2009年秋季 第70回 応用物理学会 学術講演会","2009-09-08","","jpn","oral_presentation","","","","","","","Co2FeAl(CFA)フルホイスラー合金は,バンド計算からハーフメタル特性は期待されず,実験的にはB2構造のCFA/アモルファスAlOx/CoFe構造においてスピン分極率Pは0.6程度と報告されている。本研究では,まだ報告されていないCFA/MgO/CoFeフルエピタキシャルMTJのTMR効果について検討した。" "Tunnel magnetoresistance in a Co2FeAl0.5Si0.5/(Mg,Al)Ox/CoFe magnetic tunnel junction","Co2FeAl0.5Si0.5/(Mg,Al)Ox/CoFe強磁性トンネル接合のTMR効果","シャン ロン, 介川 裕章, 王 文洪, 小塚 雅也, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","シャン ロン, 介川 裕章, 王 文洪, 小塚 雅也, 古林 孝夫, 大久保 忠勝, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","2009年秋季 第70回 応用物理学会 学術講演会","2009年秋季 第70回 応用物理学会 学術講演会","2009-09-08","","jpn","oral_presentation","","","","","","","Co2FeAl0.5Si0.5合金(CFAS)のフェルミ準位はハーフメタルギャップのほぼ中央に位置すると理論予測されており,室温でも高いスピン分極率Pが期待できる材料として実験的報告が相次いでいる[1-3]。本研究では,CFAS層のPを実験的に決定し,ハーフメタル特性についての情報を得るためにAlOxバリアとCoFe上部電極を有するMTJを作製した。【実験方法】マグネトロンスパッタ装置を用いてMgO(001)単結晶基板上にCr(40)/CFAS(80)/(Mg,Al)Ox/CoFe(3)/IrMn(12)/Ru(7),(単位:nm)の多層膜を作製した。バリア層作製にはICP酸化を用い,下部層への酸化中のダメージを低減させるため極薄Mg層をAl層下に挿入した。微細加工により1515 m2に素子を加工し,直流4端子法により磁気伝導特性を評価した。" "Effects of spin accumulation in a double tunnel junction: Simple model calculations","2重トンネル接合におけるスピン蓄積の効果:簡易モデルによる計算","三谷 誠司, 葛西 伸哉, 介川 裕章","三谷 誠司, 葛西 伸哉, 介川 裕章","応用物理学会学術講演会","応用物理学会学術講演会","2009-09-08","","jpn","oral_presentation","","","","","","","強磁性2重トンネル接合は種々の機能特性を有しており、スピントロニクス分野における重要な研究対象のひとつとなっているが、スピン蓄積に関する研究は少ない。本研究では、2重接合におけるスピン蓄積の効果を調べることを目的とし、まず最初にJulliereモデルを2重接合に拡張した簡単なモデルによって、スピン蓄積がトンネル磁気抵抗効果(TMR)などに及ぼす影響について調べた。" "Current-induced magnetization switching in CPP-GMR devices with full-Heusler Co2FeAl0.5Si0.5 alloys","フルホイスラー合金Co2FeAl0.5Si0.5を用いたCPP-GMR素子のスピン注入磁化反転","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","介川 裕章, 葛西 伸哉, 古林 孝夫, 三谷 誠司, 猪俣 浩一郎","2009年秋季 第70回 応用物理学会 学術講演会","2009年秋季 第70回 応用物理学会 学術講演会","2009-09-08","","jpn","oral_presentation","","","","","","","スピン注入磁化反転はMRAMなどの情報書き込み技術として盛んに研究がなされている。しかし,応用の観点から反転電流密度Jcの低減が求められている。理論的には,高スピン偏極材料を強磁性電極として用いることでJcの低減が期待できるため,本研究では高スピン偏極材料としてCo2FeAl0.5Si0.5(CFAS)を用い,CFAS/Ag/CFAS構造のCPP-GMR素子を作製しスピン注入磁化反転観察を試みた。" "Tunnel Magnetoresistance in Full-Heusler Co2FeSi0.5Al0.5/MgO/Co2FeSi0.5Al0.5 Magnetic Tunnel Junctions","Tunnel Magnetoresistance in Full-Heusler Co2FeSi0.5Al0.5/MgO/Co2FeSi0.5Al0.5 Magnetic Tunnel Junctions","介川 裕章, 中谷 友也, 王 文洪, シャン ロン, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, 中谷 友也, 王 文洪, シャン ロン, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","International Conference on Magnetism (ICM)","International Conference on Magnetism (ICM)","2009-07-26","","jpn","oral_presentation","","","","","","","Co-based full-Heusler Co2FeSi0.5Al0.5 (CFAS) alloys have attracted great attention as a promising candidate of the half-metal at room temperature. In this study, we perform a high TMR ratio at RT using a Co2FeSi0.5Al0.5/MgO/Co2FeSi0.5Al0.5 magnetic tunnel junction. By optimizing deposition condition of the MgO barrier, we achieved TMR ratio of 223% at RT (431% at 7 K). Cross-sectional high-resolution transmission electron microscopy images show that both the bottom and top CFAS layers have B2 structure and fully-epitaxial growth is achieved throughout the whole MTJ stack. We can expect a higher TMR ratio if ordering parameter of the CFAS layer is improved." "HIGH TUNNEL MAGNETORESISTANCE IN FULLY-EPITAXIAL MAGNETIC TUNNEL JUNCTIONS WITH FULL HEUSLER Co2FeAl0.5Si0.5 ALLOYS","HIGH TUNNEL MAGNETORESISTANCE IN FULLY-EPITAXIAL MAGNETIC TUNNEL JUNCTIONS WITH FULL HEUSLER Co2FeAl0.5Si0.5 ALLOYS","介川 裕章, 中谷 友也, 王 文洪, シャン ロン, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","介川 裕章, 中谷 友也, 王 文洪, シャン ロン, 三谷 誠司, 猪俣 浩一郎, 宝野 和博","20th International Colloquiumon Magnetic Films and Surfaces","20th International Colloquiumon Magnetic Films and Surfaces","2009-07-20","","jpn","oral_presentation","","","","","","","Co-based full-Heusler Co2YZ alloys with L21 structure have attracted great attention as a promising candidate of the half-metal due to both the fully spin polarized band structures and high Curie temperatures around 1,000 K. In order to maximize the true potential of the half-metallicity of the CFAS in a MTJ structure, a high quality tunnel barrier without structural imperfections is required. In this study we focused on the MgO barrier formation method; sputtering and electron-beam evaporation, to optimize the structure of the tunnel barrier and to obtain a higher TMR ratio in the CFAS/MgO/CFAS MTJs." "Development of half metallic Heusler alloys and applications to CPP-GMR","ハーフメタルホイスラー合金の材料開発とCPP-GMRへの応用","古林 孝夫, 小玉 恒太, 中谷 友也, ボラプラガダ バラプラサド, アマナボルル ラジニカンス, サンカール ビジェイカルシック, 高橋 有紀子, 介川 裕章, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 小玉 恒太, 中谷 友也, ボラプラガダ バラプラサド, アマナボルル ラジニカンス, サンカール ビジェイカルシック, 高橋 有紀子, 介川 裕章, 猪俣 浩一郎, 宝野 和博","第30回ナノマグネティックス専門研究会","第30回ナノマグネティックス専門研究会","2009-06-26","","jpn","oral_presentation","","","","","",""," Co基ホイスラー合金について,点接触アンドレーフ反射法によってスピン分極率の測定を行いハーフメタルの探索をおこなった.いくつかの3元ホイスラー合金について,第4元素の添加によってスピン分極率が上昇することが示された.また,トンネル接合において高いMR比が得られているホイスラー合金、Co2FeAl0.5Si0.5 (CFAS)及びCo2MnSi(CMS)を強磁性電極としてAgをスペーサ層に用いたCPP-GMR素子を作製し、大きなMR比を得た。" "Microstructure, magnetic and transport properties of Co-ferrite thin films ","Microstructure, magnetic and transport properties of Co-ferrite thin films ","高橋 有紀子, 関剛斎, 介川 裕章, 古林 孝夫, 三谷 誠司, 高梨弘毅, 猪俣 浩一郎, 宝野 和博","高橋 有紀子, 関剛斎, 介川 裕章, 古林 孝夫, 三谷 誠司, 高梨弘毅, 猪俣 浩一郎, 宝野 和博","2009 Intermag","2009 Intermag","2009-05-04","","jpn","oral_presentation","","","","","","","A spin filtering device with a ferromagnetic insulator has received much attention to produce highly spin-polarized current. As the tunneling probability depends exponentially on the barrier height, a ferromagnetic insulator could be a very efficient spin filter and thus a large TMR in a spin filter junction is expected. Co ferrite is one of the candidates as the ferromagnetic insulaters of spin filtering devices due to its high Currie temperature; however, the large spin filtering effect at room temperautre has not been reported so far[1]. For a highly efficient spin filter effect at RT, we made a top pin type spin-valve structure with a Co ferrite thin layer. " "Development of Heusler materials and high ΔR/R in CPP-GMR","ホイスラー合金材料とそれを用いた高磁気抵抗比CPPGMR 素子の開発","古林 孝夫, 小玉 恒太, 中谷 友也, 介川 裕章, 高橋 有紀子, シャン ロン, 王 文洪, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 小玉 恒太, 中谷 友也, 介川 裕章, 高橋 有紀子, シャン ロン, 王 文洪, 猪俣 浩一郎, 宝野 和博","IEEE International Magnetics Conference","IEEE International Magnetics Conference","2009-05-04","","jpn","oral_presentation","","","","","","","High spin polarization of half metallic Housler alloys is believed effective for current-perpendicular-to-plane giant magnetoresistance (CPP GMR). This paper reports the CPP GMR of spin valves with two kinds of Heusler alloys, CoFeAl0.5Si0.5 (CFAS) and Co2MnSi (CMS), as ferromagnetic electrodes. Multilayer stacks based on the trilayer GMR structures, CFAS/Ag/CFAS, CMS/Ag/CMS and CMS/Cu/CMS were prepared. The epitaxial growth of the films up to the top Hesler layers was confirmed by TEM observations in each combination. Large MR ratio up to 12% at room temperature and 30% at 10 K were achieved. The high spin polarization of the epitaxial Heusler layers is the most likely origin of the high MR ratio." "CPP-GMR using epitaxial films of Heusler alloys","ホイスラー合金エピタキシャル膜を用いたCPP-GMR素子の作製","古林 孝夫, 中谷 友也, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 中谷 友也, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","2009年(平成21年)春季第56回応用物理学関係連合講演会","2009年(平成21年)春季第56回応用物理学関係連合講演会","2009-03-30","","jpn","oral_presentation","","","","","",""," トンネル接合において高いMR比が得られているホイスラー合金、Co2FeAl0.5Si0.5 (CFAS)及びCo2MnSi(CMS)を強磁性電極として用いたCPP-GMR素子を作製し、そのMR特性を調べた。  CFASを用いたCPP-GMR素子の積層構造は下からCr(10)/Ag(200)/CFAS(20)/Ag(5)/CFAS(5)/CoFe(2)/IrMn(10)/Ru(8)(数字は厚さ、nm)であり、下部及び上部CFAS層をスパッタした後、それぞれ400˚Cでのアニールを行った。断面TEM観察により上部CFAS層までのエピタキシャル成長が確認された。室温でMR比12.4%、面積×抵抗値、RA =0.121 Ω(μm)2、抵抗変化量 ΔRA =15 mΩ(μm)2が得られた。MSを用いたCPP-GMR素子においては、Cu及びAgをスペーサ層に用いた場合に室温でそれぞれ8.5%、10.5%のMR比が得られた。" "Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunneling junctions on thermally oxidized Si substrates","熱酸化膜付Si基板上に作製したCo2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5強磁性トンネル接合","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","2009年春季第56回応用物理学関係連合講演会","2009年春季第56回応用物理学関係連合講演会","2009-03-30","","jpn","oral_presentation","","","","","","","筆者らはこれまでフルホイスラー合金Co2FeAl0.5Si0.5(CFAS)を用いた強磁性トンネル接合(MTJ)において、大きなTMRを報告してきた1)-3)。しかし,いずれも高価なMgO単結晶基板上に作製しており,実用化に向けた問題の一つとなっている。本研究では熱酸化膜付Si基板上に高(001)配向したCFAS層を実現し,高TMR比の可能性を調べた。" "Tunnel magnetoresistance in full-Heusler Co2FeAl0.5Si0.5-based magnetic tunnel junctions","フルホイスラーCo2FeAl0.5Si0.5合金を用いた強磁性トンネル接合のTMR効果","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","2009年春季 第56回応用物理学関係連合講演会","2009年春季 第56回応用物理学関係連合講演会","2009-03-30","","jpn","oral_presentation","","","","","","","筆者らはCo2FeAl0.5Si0.5(CFAS)合金を用いた強磁性トンネル接合(MTJ)において大きなトンネル磁気抵抗(TMR)1)を報告してきた。高いTMR比を得るためには,電極であるホイスラー合金層の規則度の向上に加え,バリア層およびバリア/電極界面の結晶性の向上も非常に重要である。本研究ではスパッタ法(スパッタ素子)と電子線蒸着法(EB素子)の2つの方法でMgOバリア層を作製し,高TMR比実現の指針を得ることを目的とした。" "CPP-GMR usingCo2FeAl0.5Si0.5 Heusler alloy ","ホイスラー合金Co2FeAl0.5Si0.5を用いたCPP-GMR素子の作製と伝導特性","古林 孝夫, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","2009年日本金属学会春期(第144回)大会","2009年日本金属学会春期(第144回)大会","2009-03-28","","jpn","oral_presentation","","","","","","","ホイスラー合金,Co2FeAl0.5Si0.5(CFAS)を強磁性電極として用いたCPP-GMR素子を作成した.薄膜はCr(10)/Ag(200)/CFAS(20)/Ag(5)/CFAS(5)/CoFe(2)/IrMn(10)/Ru(8)(数字は厚さ,nm)の構造である.電子ビームリソグラフィーとArイオンエッチングによって微細加工を行いCPP-GMR素子とした.室温でMR比12.4%、面積×抵抗値、RA =0.121 Ω(μm)2、抵抗変化量 ΔRA =15 mΩ(μm)2が得られた。下部CFAS層のみを400˚Cでアニールした場合のMR比は6.9%であり、アニールによってCFAS層の規則構造が改善され高いMR比が得られたものと考えられる。" "CPP-GMR using Co2MnSi Heusler alloys","Co2MnSiホイスラー合金を用いたCPP-GMR","小玉 恒太, 古林 孝夫, 介川 裕章, 中谷 友也, 猪俣 浩一郎, 宝野 和博","小玉 恒太, 古林 孝夫, 介川 裕章, 中谷 友也, 猪俣 浩一郎, 宝野 和博","2009年日本金属学会春期(第144回)大会","2009年日本金属学会春期(第144回)大会","2009-03-28","","jpn","oral_presentation","","","","","","","CPP-GMR素子はTMR素子に比べ電気抵抗が低いため,次世代の高密度ハードディスクドライブ(HDD)の再生ヘッドとして実用化が期待されている.しかしながら現状のCPP-GMR素子で実現できるMR値は低く,今後300Gbit/in2を超える高密度記録に向け低電気抵抗を維持しつつ,単位体積当たりの抵抗変化量を大きくしていくことが必要である.本研究では,Co2MnSi (CMS)を強磁性層として用いたスピンバルブ構造のCPP-GMR素子を作製し,高いGMRの発現を目指した. 試料はMgO (001)単結晶基板上に室温でCr(10nm)/Ag(200 nm)/Cr(10 nm)/CMS(20 nm)/Cu(4 nm)/CMS(5 nm)/FeCo(2 nm)/IrMn(10nm)/Ru(5 nm)の多層膜を作製した.MR測定結果として,室温でMR比=8.6%,単位体積当たりの抵抗変化量RA=14.2mΩμm2 の値を示し,低温測定(6K)ではMR比=30.7%,RA=35.2mΩμm2と著しく値が増加した.CMSはGMRにおいても高いMR値を実現することを示した." "スピン偏極-イオン散乱分光法(SP-ISS)によるCo2FeAl0.5Si0.5フルホイスラー合金表面の構造とスピン状態分析","スピン偏極-イオン散乱分光法(SP-ISS)によるCo2FeAl0.5Si0.5フルホイスラー合金表面の構造とスピン状態分析","鈴木 拓, 介川 裕章, 猪俣 浩一郎","鈴木 拓, 介川 裕章, 猪俣 浩一郎","第9回「イオンビームによる表面・界面解析」特別研究会","第9回「イオンビームによる表面・界面解析」特別研究会","2008-12-05","","jpn","oral_presentation","","","","","","","本研究では、我々が開発したこのSP-ISSをCo2FeAl0.5Si0.5(CFAS)の組成のホイスラー合金薄膜の表面分析に応用した。このCFASは、理論的にPEFが1(ハーフメタル)であることが予想されており、またCFASを用いたTMR素子において室温でホイスラー合金で最高のTMR比220%が報告されている[2]。CFAS(001)表面ではCo層とFe-Al-Si層の2種類の終端層の可能性があるが、この終端層を含めてその表面構造は明らかになっていない。また、その表面スピン状態も明らかにされていない。" "Half-metallic Co2FeAl0.5Si0.5 Heusler alloys for spintronics devices ","スピントロニクスのためのCo2FeAl0.5Si0.5ホイスラー合金ハーフメタル","猪俣 浩一郎, 介川 裕章, 王 文洪, シャン ロン, 古林 孝夫, 高橋 有紀子, 宝野 和博","猪俣 浩一郎, 介川 裕章, 王 文洪, シャン ロン, 古林 孝夫, 高橋 有紀子, 宝野 和博","MRS fall meeting 2008","MRS fall meeting 2008","2008-12-01","","jpn","oral_presentation","","","","","","","The performance of spintronics depends on spin polarization of the current. Therefore, highly spin polarized current source is strongly desired in spintronics. The use of half-metallic ferromagnets (HMFs) is a typical approach for this purpose. HMFs are characterized by a metallic density of states at Fermi level (EF) for one spin channel, while the states for the other spin channel display a gap at EF, leading to 100% spin polarization. Among some kinds of HMFs Co-based full-Heusler alloys with a chemical form of Co2YZ and L21 structure have been growingly investigated since a large tunneling magnetoresistance (TMR) observation at RT using a Co2Cr0.6Fe0.4Al (CCFA) electrode in magnetic tunnel junctions (MTJs)1). Recently, we have reported very large TMR up to 220% at RT for an epitaxial C" "Tunnel magnetoresistance in Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunneling junctions prepared on thermally oxidized Si substrates with MgO buffer","Tunnel magnetoresistance in Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunneling junctions prepared on thermally oxidized Si substrates with MgO buffer","王 文洪, 介川 裕章, シャン ロン, 猪俣 浩一郎","王 文洪, 介川 裕章, シャン ロン, 猪俣 浩一郎","the 53rd Annual Conference on Magnetism and Magnetic Materials ","the 53rd Annual Conference on Magnetism and Magnetic Materials ","2008-11-09","","jpn","oral_presentation","","","","","","","Magnetic tunnel junction (MTJs) using polycrystalline Co2FeAl0.5Si0.5 (CFAS) electrodes with an MgO tunnel barrier were fabricated onto thermally oxidized Si substrates. A highly (001)-oriented and B2-type ordered CFAS electrodes were obtained by optimizing the post-annealing temperature, The microfabricated MTJs exhibited relatively high tunnel magnetoresistance ratios of 125 % at room temperature and 196 % at 7 K. A high tunneling spin polarization of 0.7 at 7 K was estimated for the polycrystalline B2-ordered CFAS electrodes." "Tunnel magnetoresistance effect and tunneling conductance in magnetic tunnel junctions with full-Heusler Co2FeAl0.5Si0.5 electrodes","Tunnel magnetoresistance effect and tunneling conductance in magnetic tunnel junctions with full-Heusler Co2FeAl0.5Si0.5 electrodes","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","53rd Annual Conference on Magnetism and Magnetic Materials ","53rd Annual Conference on Magnetism and Magnetic Materials ","2008-11-11","","jpn","oral_presentation","","","","","","","A group of Co-based full-Heusler alloys with Co2XY type is the most promising candidate due to their high Curie temperature, which is expected to bring half-metallicity even at room temperature. In order to achieve higher TMR ratio, it is important to explore the conditions for obtaining half-metallicity of CFAS and investigate the effect of the disorder on both spin polarization and density of states. In this study we demonstrate the half-metallicity of L21-CFAS and the direct tunneling between the half-metallic L21-CFAS electrodes by analyzing the bias voltage dependence of differential tunneling conductance G = dI/dV measured for epitaxial L21-CFAS/MgO/L21-CFAS MTJs using the specific DOS of half-metallic L21-CFAS obtained from the first principle calculations." "Current-perpendicular-to-plane giant magnetoresistance of a spin valve using Co2MnSi Heusler alloy electrodes","Co2MnSiホイスラー合金を用いたスピンバルブのCPP‐GMR","小玉 恒太, 古林 孝夫, 中谷 友也, 介川 裕章, 猪俣 浩一郎, 宝野 和博","小玉 恒太, 古林 孝夫, 中谷 友也, 介川 裕章, 猪俣 浩一郎, 宝野 和博","53rd Annual Conference on Magnetism and Magnetic Materials","53rd Annual Conference on Magnetism and Magnetic Materials","2008-11-11","","jpn","oral_presentation","","","","","","","We report the current-perpendicular-to-plane giant magnetoresistance of a spin valve with Co2MnSi (CMS) Heusler alloy ferromagnetic electrodes. A multilayer stack of Cr/Ag/Cr/CMS/Cu/CMS/Fe25Co75/Ir28Mn72/Ru was deposited on a MgO (001) single crystal substrate. The bottom CMS layer was epitaxially grown on the Cr/Ag/Cr buffer layers and was ordered to the L21 structure after annealing at 673 K. The upper CMS layer was found to grow epitaxially on the Cu spacer layer despite the large lattice mismatch between Cu and CMS. The highest MR ratios of 8.6% and 30.7% for CPP-GMR were recorded at room temperature and 6 K, respectively. The high spin polarization of the epitaxial CMS layers is the most likely origin of the high MR ratio." "Current-perpendicular-to-plane giant magnetoresistance in spin-valve structures using epitaxial Co2FeAl0.5Si0.5 /Ag/ Co2FeAl0.5Si0.5 trilayers","ホイスラー合金Co2FeAl0.5Si0.5エピタキシャル膜によるCPP-GMR","古林 孝夫, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","53rd Annual Conference on Magnetism and Magnetic Materials","53rd Annual Conference on Magnetism and Magnetic Materials","2008-11-11","","jpn","oral_presentation","","","","","","","A current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin valve using epitaxial layers of Co2FeAl0.5Si0.5 (CFAS) Heusler alloy as ferromagnetic electrodes is reported. A multi-layer stack of Cr/Ag/CFAS/Ag/CFAS/Co75Fe25/Ir22Mn78/Ru was deposited on a MgO (001) single crystal substrate. Epitaxial growth of the Cr, Ag and CFAS layers in the (001) orientation up to the top CFAS layer was confirmed. Large MR ratios of 6.9 % at room temperature and 14 % at 6 K were observed for the CPP-GMR device. High spin polarization of epitaxial CFAS is the possible reason for the high MR ratios." "CPP-GMR using epitaxial layers of Heusler alloy Co2FeAl0.5Si0.5","ホイスラー合金Co2FeAl0.5Si0.5エピタキシャル膜によるCPP-GMR","古林 孝夫, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","古林 孝夫, 小玉 恒太, 介川 裕章, 高橋 有紀子, 猪俣 浩一郎, 宝野 和博","第32回日本磁気学会学術講演会","第32回日本磁気学会学術講演会","2008-09-12","","jpn","oral_presentation","","","","","","","ホイスラー合金,Co2FeAl0.5Si0.5(CFAS)を強磁性電極として用いたCPP-GMR素子を作成した.薄膜はCr(10)/Ag(200)/CFAS(20)/Ag(5)/CFAS(5)/CoFe(2)/IrMn(10)/Ru(8)(数字は厚さ,nm)の構造である.電子ビームリソグラフィーとArイオンエッチングによって0.3μm×0.6μmの大きさに微細加工を行いCPP-GMR素子とした.室温で6.7%、6Kで14%のMR比が得られた.今後種々の条件の最適化,特にCFASの構造の規則度を上げることによりさらなる特性の向上を目指す." "Spin-Polarized Tunneling Spectroscopy in Fully Epitaxial Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 Magnetic Tunnel Junctions","フルエピタキシャルCo2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 強磁性トンネル接合のスピン偏極トンネル分光","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","第32回日本磁気学会学術講演会","第32回日本磁気学会学術講演会","2008-09-12","","jpn","oral_presentation","","","","","","","高いキュリー点を有するCo基フルホイスラー合金(Co2YX)は,室温で高いスピン分極率を持つハーフメタル材料の候補として注目を集めている。近年,Co2FeAl0.5Si0.5(CFAS)合金を用いた強磁性トンネル接合(MTJ)において,室温で220%の大きなトンネル磁気抵抗(TMR)比が報告されており,高いL21規則度,高品質なトンネルバリア/CFAS界面を実現できれば,より高いTMR比,すなわち高スピン分極率の実現が期待できる。本研究では,高スピン分極率の実現の指針を得るため,規則度が異なるCFAS層を有するCFAS/ MgO/CFAS構造を作製し,TMR特性および,トンネルコンダクタンス特性の解析を行った。トンネルコンダクタンス特性には電極材料のバンド構造が強く反映されるため,CFAS層のハーフメタル特性や規則度によるバンド構造の違いを明らかにできる。" "Epitaxial growth of Co2FeAl0.5Si0.5 thin films on MgO substrates: Structural, magnetic, and transport properties","Epitaxial growth of Co2FeAl0.5Si0.5 thin films on MgO substrates: Structural, magnetic, and transport properties","王 文洪, 介川 裕章, シャン ロン, 猪俣 浩一郎","王 文洪, 介川 裕章, シャン ロン, 猪俣 浩一郎","To attend the 32nd Annual Conference on MAGNETICS in Japan ","To attend the 32nd Annual Conference on MAGNETICS in Japan ","2008-09-12","","jpn","oral_presentation","","","","","","","Full-Heusler alloy Co2FeSi0.5Al0.5 (CFAS) has been proposed as a promising candidate to become a robust half-metallic ferromagnet even at room temperature, because its EF is theoretically predicted to lie at the middle of the minority gap, which enhances the temperature stability of the spin polarization. In this study, we achieved a highly L21-ordered full-Heusler alloy CFAS thin film using an MgO buffer layer instead of the Cr buffer layer, and investigated its structure, magnetic and transport properties as a function of post-annealing temperature. " "CPP-GMR of multilayered films using Co2MnSi Heusler alloys","Co2MnSiホイスラー合金を用いたCPP‐GMR","小玉 恒太, 古林 孝夫, 中谷 友也, 介川 裕章, 猪俣 浩一郎, 宝野 和博","小玉 恒太, 古林 孝夫, 中谷 友也, 介川 裕章, 猪俣 浩一郎, 宝野 和博","第32回日本磁気学会学術講演会","第32回日本磁気学会学術講演会","2008-09-12","","jpn","oral_presentation","","","","","","","ホイスラー合金,Co2MnSi(CMS)を強磁性電極として用いたCPP-GMR素子を作成した.薄膜はCr(10nm)/Ag(200 nm)/Cr(10 nm)/CMS(20 nm)/Cu(4 nm)/CMS(5 nm)/FeCo(2 nm)/IrMn(10 nm) /Ru(5 nm)の構造である.電子ビームリソグラフィーとArイオンエッチングによって0.51×0.95μm2の大きさに微細加工を行いCPP-GMR素子とした.室温で8.6%、6Kで30.7%のMR比が得られた.今後、強磁性層の厚さなど種々の要因を試すことにより、さらに大きなMR値が得られると考えられる。" "Tunneling Conductance in Magnetic Tunnel Junctions with Full-Heusler Co2FeAl0.5Si0.5 Electrodes","フルホイスラーCo2FeAl0.5Si0.5合金を用いた強磁性トンネル接合のトンネルコンダクタンス","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","第69回応用物理学会学術講演会","第69回応用物理学会学術講演会","2008-09-02","","jpn","oral_presentation","","","","","","","フルホイスラー合金Co2FeAl0.5Si0.5(CFAS)はバンド計算からハーフメタルであることが理論予測されており,実験的に高いTMR比が室温で報告されている。本研究では,CFAS/MgO/CFAS構造を持つ強磁性トンネル接合を作製し,その微分コンダクタンスを評価することでCFAS膜のバンド構造を明らかにすることを目的とした。マグネトロンスパッタ装置を用いてフルエピタキシャルMgO/L21-CFAS/MgO/L21-CFAS構造を作製した。結果として7 Kで最大308%の大きなTMR比が得られた。また,微分コンダクタンス曲線はバイアス電圧に対し対称であり,平行と反平行配列時のそれぞれの曲線が明瞭に二つのバイアス電圧で交差する様子が観測された。このような振る舞いは異なる多層膜構造では観測されず,作製したL21-CFAS層は,理論計算されたハーフメタルバンド構造を持つと仮定することで説明できる。" "Structural and Magnetic Properties of Full-Heusler Co2FeAl0.5Si0.5 Thin Films on MgO-Buffered MgO Substratesdai","MgO基板/MgOバッファ層上に作製したCo2FeAl0.5Si0.5フルホイスラー合金の結晶構造および磁気特性","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","第69回応用物理学会学術講演会","第69回応用物理学会学術講演会","2008-09-02","","jpn","oral_presentation","","","","","","","L21構造を有するフルホイスラー合金Co2FeAl0.5Si0.5(CFAS)を用いた強磁性トンネル接合(MTJ)において,室温で220%の大きなTMR比が実現され注目を集めている。この研究ではCrバッファーが用いられており,高温熱処理によりCr原子がCFAS層に拡散するため,高いL21規則度を得ることの障害となっていた。本研究では,バッファ層としてCrの代わりにMgOを採用することで,高いL21規則度および良好な磁気特性を得ることを目的とした。マグネトロンスパッタ装置を用いてMgO(001)単結晶基板上に,MgOをバッファとしてCFAS層を30 nm成膜した。成膜後,真空中熱処理を行い,CFAS膜の結晶性および磁気特性を評価した。XRDパターンから,Ta= 550 C以上でL21規則化が始まり,Ta上昇とともに規則度が増大する様子が得られた。" "Structure and magnetic properties of epitaxial full-Heusler alloy Co2FeAl0.5Si0.5 films on MgO-buffered MgO (001) substrates and TMR using their electrodes","MgOバッファ層上のエピタキシャルフルホイスラー合金Co2FeAl0.5Si0.5薄膜の構造,磁気およびTMR特性","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","介川 裕章, 王 文洪, シャン ロン, 猪俣 浩一郎","IEEE Magnetics Conference (INTERMAG 2008)","IEEE Magnetics Conference (INTERMAG 2008)","2008-05-04","","jpn","oral_presentation","","","","","","","Half-metals is an ideal material for spintronics devices, such as spin MOSFETs and high density nonvolatile memory devices. Recently, Co-based full-Heusler alloys have attracted great attention as promising candidates of the half-metals. Very recently, a large TMR ratio as high as 220% at RT has been reported in a MgO(001)/Cr-buffer/Co2FeSi0.5Al0.5 (CFAS)/MgO/CFAS magnetic tunnel junction (MTJ) . However, Cr buffer impedes a highly L21-ordered structure due to the Cr interdiffusion by post-deposition annealing at a high temperature . In this study we achieved a highly L21-ordered CFAS layer using an MgO buffer layer instead of a Cr buffer layer, and investigated structure and magnetic and TMR properties as a function of post-deposition annealing temperature." "Achievement of Highly L21 Ordered Full-Heusler Co2Fe(Si0.5Al0.5) Thin Films","高L21規則度を有するCo2FeSi0.5Al0.5フルホイスラー合金の作製","介川 裕章","介川 裕章","MANA International Symposium 2008 & ICYS Workshop 2008","MANA International Symposium 2008 & ICYS Workshop 2008","2008-03-10","","jpn","oral_presentation","","","","","","","The usage of electron’s spin is expected to provide additional functionality and higher performance in electronics, including a spin transistor and low consumption nonvolatile memory devices (spintronics devices). Halfmetal, which has 100% spin polarized conduction electron band, is an ideal material for establishing the spintronics devices. Especially, Co-based full-Heusler alloys (Co2XY type L21 structure) have attracted great attention as promising candidates of the halfmetal due to both the fully spin polarized band structures and high Curie temperatures. Recently, a large tunnel magnetoresistance (TMR) ratio (220% at room temperature (RT), 390% at 5 K) has been reported in a Cr-buffer/Co2Fe(Si0.5Al0.5)/MgO /Co2Fe(Si0.5Al0.5) magnetic tunnel junction. However, it is difficult to obtai" "Structure and TMR properties of the junctions using Co-based full-Huesler alloy electrodes","Co基フルホイスラー合金を電極に用いたトンネル接合の構造とTMR特性","猪俣 浩一郎, 池田直路, 手束展規 , Marek Wojcik, Eva Jedryka, シャン ロン, 介川 裕章","猪俣 浩一郎, 池田直路, 手束展規 , Marek Wojcik, Eva Jedryka, シャン ロン, 介川 裕章","2008 International Conference on Nanoscience and Nanotechnology ","2008 International Conference on Nanoscience and Nanotechnology ","2008-02-25","","jpn","oral_presentation","","","","","","","Very recently, we have reported the very large TMR at RT up to 220% for the spin valve-type MTJ using Co2FeSi0.5Al0.5 (CFSA) full-Heusler films for top and bottom electrodes and a MgO (001) barrier formed on a Cr-buffered MgO (001) single crystal substrate[7]. In this work we study the disorder structure of CFSA films using 59Co NMR and discuss its dependence on the TMR using CFSA electrodes. " "Structure and TMR properties of the junctions using Co-based full-Heusler alloy electrodes","Co基フルホイスラー合金を電極に用いたトンネル接合の結晶構造とTMR特性","猪俣 浩一郎, 池田直路, 手束展規, 杉本諭, Marek Wojcik, シャン ロン, 介川 裕章, 古林 孝夫","猪俣 浩一郎, 池田直路, 手束展規, 杉本諭, Marek Wojcik, シャン ロン, 介川 裕章, 古林 孝夫","第31回日本応用磁気学会学術講演会","第31回日本応用磁気学会学術講演会","2007-09-11","","jpn","oral_presentation","","","","","","","The relatively large TMR at room temperature (RT) have been reported recently by using Co-based full-Heusler alloys in MTJs. These investigations employed the Heusler alloys only for the bottom electrode on a MgO (001) substrate, because a highly ordered B2 or L21 structure of the Heusler alloys is difficult to be made on a barrier, although it is easily fabricated on a single crystal MgO(001) substrate or a metallic buffer layer such as Cr. Very recently, we have reported 220% TMR at RT for the spin valve-type MTJ with Co2Fe Si0.5Al0.5 (CFSA) full-Heusler films for top and bottom electrodes and a MgO (001) barrier formed on a Cr-buffered MgO (001) single crystal substrate. In this work we show more detail and discuss the relation between TMR and the structure of CFSA." "Tunnel Magnetoresistance Enhancement within Cotunneling Region in a Magnetic Tunnel Junction with a Nano-Particle Layer","Tunnel Magnetoresistance Enhancement within Cotunneling Region in a Magnetic Tunnel Junction with a Nano-Particle Layer","介川 裕章, 猪俣 浩一郎","介川 裕章, 猪俣 浩一郎","1st NIMS Conference on Recent Breakthroughs in Materials Science","1st NIMS Conference on Recent Breakthroughs in Materials Science","2007-07-11","","jpn","oral_presentation","","","","","","","Coulomb blockade (CB) is expected to be the principle of future single-electron devices, and a number of studies have been reported including a tunnel magnetoresistance (TMR) effect. Takahashi and Maekawa predicted a TMR enhancement due to the cotunneling process in an ultra-small double tunnel junction (DTJ) [Phys. Rev. Lett. 80, 1758 (1998)]. In this study, we have fabricated a DTJ with a ferromagnetic nano-particle layer (hybrid junction) and observed the enhancement of TMR ratio within the CB region. The TMR ratio increases greatly from 10% to 24% near zero bias voltage at 7 K. The enhancement of the TMR ratio disappears at RT. These findings agree well with theoretical prediction proposed by Takahashi and Maekawa."