"published_papers" "Title(English)","Title(Japanese)","Author(s)(English)","Author(s)(Japanese)","Journal name(English)","Journal name(Japanese)","Volume","Number","First page","Last page","Date of publication","Peer reviewed/Not peer reviewed","Invited/Not invited","Publishing type","Language","ISSN","DOI","URL","Description(English)","Description(Japanese)" "Antiferromagnetic Films and Their Applications","Antiferromagnetic Films and Their Applications","Atsufumi Hirohata, David C. Lloyd, Takahide Kubota, Takeshi Seki, Koki Takanashi, Hiroaki Sukegawa, Zhenchao Wen, Seiji Mitani, Hiroki Koizumi","Atsufumi Hirohata, David C. Lloyd, Takahide Kubota, Takeshi Seki, Koki Takanashi, Hiroaki Sukegawa, Zhenchao Wen, Seiji Mitani, Hiroki Koizumi","IEEE Access","IEEE Access","11","","117443","117459","2023","TRUE","","scientific_journal","eng","","10.1109/access.2023.3326448","","Spintronic devices are expected to replace the recent nanoelectronic memories and sensors due to their efficiency in energy consumption and functionality with scalability. To date, spintronic devices, namely magnetoresistive junctions, employ ferromagnetic materials by storing information bits as their magnetization directions. However, in order to achieve further miniaturization with maintaining and/or improving their efficiency and functionality, new materials development is required: 1) increase in spin polarization of a ferromagnet or 2) replacement of a ferromagnet by an antiferromagnet. Antiferromagnetic materials have been used to induce an exchange bias to the neighboring ferromagnet but they have recently been found to demonstrate a 100% spin-polarized electrical current, up to THz oscillation and topological effects. In this review, the recent development of three types of antiferromagnets is summarized with offering their future perspectives towards device applications.","" "Nano-crystal domains in Co-based fcc(111) epitaxial magnetic junctions and their impact on tunnel magnetoresistance","Nano-crystal domains in Co-based fcc(111) epitaxial magnetic junctions and their impact on tunnel magnetoresistance","Cong He, Keisuke Masuda, Jieyuan Song, Thomas Scheike, Zhenchao Wen, Yoshio Miura, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani, Hiroaki Sukegawa","Cong He, Keisuke Masuda, Jieyuan Song, Thomas Scheike, Zhenchao Wen, Yoshio Miura, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani, Hiroaki Sukegawa","Acta Materialia","Acta Materialia","261","","119394","","2023-12-01","TRUE","","scientific_journal","eng","","10.1016/j.actamat.2023.119394","","Nano-crystal domain structures formed in a MgO barrier and their effects on tunnel magnetoresistance (TMR) in epitaxial fcc-Co90Fe10 (CoFe)(111)/MgO(111)/CoFe(111) magnetic tunnel junctions (MTJs) have been systematically studied using scanning transmission electron microscopy and first-principles calculations. These domains are widely distributed in the (111)-textured MgO layer, being different from conventional bcc-CoFe/MgO(001)-based MTJs. The (111)-texture is formed by extension of {111} planes through several adjacent MgO domains. Three types of orientation relationships (ORs) between CoFe and MgO are identified, including cube-on-cube type (Type-1), twin-like type (Type-2), and unexpected type (Type-3). Crystallographic analysis indicated that Type-2 OR is a variant of Type-1 OR, triggered by different stacking orders of MgO(111) planes, while Type-3 OR is formed by a 30◦ in-plane rotation of MgO lattice relative to Type-1 OR. Due to the large in-plane lattice mismatch (19.6%) between Co(111) and MgO(111) in Type-1 and Type-2 ORs, Type-3 OR (mismatch 3.4%) can be stabilized. First-principles calculations uncovered that the theoretical TMR ratio of the MgO(111) MTJ with Type-3 OR is ~2 orders of magnitude smaller than that with Type-1 and Type-2 ORs. The small contribution of Type-3 OR to the transport reasonably interprets why the experimental TMR ratio (~37%) is much lower than the theoretical value (~2100%) in the Co/MgO/Co(111) MTJ. This study has revealed the nano-crystal domain formation unique to the fcc-CoFe/MgO(111) MTJs, indicating that controlling the nano-crystal domains (e.g., lattice optimization by atomic doping) can be a guiding principle to develop MgO(111)-based epitaxial MTJs and related heterostructure devices.","" "Large magnetocapacitance of up to 456% at room temperature in FeCo/MgAl2O4/FeCo(001) magnetic tunnel junctions","Large magnetocapacitance of up to 456% at room temperature in FeCo/MgAl2O4/FeCo(001) magnetic tunnel junctions","Yuto Shibata, Kenta Sato, Hiroaki Sukegawa, Hideo Kaiju","Yuto Shibata, Kenta Sato, Hiroaki Sukegawa, Hideo Kaiju","Applied Physics Express","Applied Physics Express","16","11","113003","","2023-11-01","TRUE","","scientific_journal","eng","","10.35848/1882-0786/ad0b40","","Tunnel magnetocapacitance (TMC) ratios greater than 450% are observed at room temperature in epitaxial FeCo/MgAl2O4/FeCo(001) magnetic tunnel junctions (MTJs). A high TMC is observed at a low bias of 75 mV, which is suitable for low-power electronics. The fitting results between experimental data and calculation based on extended Debye–Fröhlich model reveal that the high TMC ratio is obtained owing to the high spin polarization of FeCo and the spin capacitance of the lattice-matched interface between FeCo and MgAl2O4. Based on this model, a TMC ratio could reach 1500% in MTJs with a spin polarization of 90%","" "Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control","Charge-to-spin conversion in fully epitaxial Ru/Cu hybrid nanolayers with interface control","Jieyuan Song, Cong He, Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Tadakatsu Ohkubo, Yukio Nozaki, Seiji Mitani","Jieyuan Song, Cong He, Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Tadakatsu Ohkubo, Yukio Nozaki, Seiji Mitani","Nanotechnology","Nanotechnology","34","36","365704","","2023-09-03","TRUE","","scientific_journal","eng","","10.1088/1361-6528/acda36","","We report on fully epitaxial Ru/Cu heterostructures fabricated with interface engineering and nanolayer insertions consisting of Cu (1nm)/Ru (1nm) structures with different numbers of periods. The atomically controlled interface was confirmed by the high-resolution high-angle annular dark-field scanning transmission electron microscopy, and the epitaxial relationship persists even in the hybrid nanolayer insertion structures. The spin current generation was detected by the measurement of unidirectional spin Hall magnetoresistance, and the effective damping-like spin Hall efficiency (ξ_DL) was further quantitatively evaluated by the spin-torque ferromagnetic resonance with thickness dependence of the ferromagnetic layer. It is found that the sharp interface Ru/Cu film has a sizeable ξ_DL of −2.2% and the insertion of Cu/Ru nanolayers at the interface can increase the ξ_DL value to −3.7%. The former could be attributed to the interface spin-orbit filtering effect and the latter may be further understood by the intrinsic contribution from the local electronic structure tuning due to the lattice distortion near the interface. A large effective spin Hall conductivity is achieved to be (3~5)×10^5 ℏ/2eΩ^(−1)m^(−1) in the epitaxial Ru/Cu hybrid nanolayers, which is in the same range as that of platinum. ","" "Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films","Spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films","Hayato Nakayama, Taisuke Horaguchi, Cong He, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuto Yamanoi, Yukio Nozaki","Hayato Nakayama, Taisuke Horaguchi, Cong He, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuto Yamanoi, Yukio Nozaki","Physical Review B","Physical Review B","107","17","","","2023-05-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.107.174416","","We experimentally demonstrate spin-torque generation using a compositional gradient at the interface between titanium and tungsten thin films. The width of the compositional gradient interface (CGI) between films is varied from 1.4 to 2.0 nm via sputtering. Spin-torque ferromagnetic resonance is observed in the ferromagnetic Ni95Cu5 alloy fabricated on a Ti/W bilayer with the CGI. The positive spin torque increases with decreasing CGI width, but a negative spin torque is superimposed owing to the negative spin Hall effect in bulk tungsten. A structural undulation in the CGI eliminates this variation in positive spin torque. The CGI width dependence of the spin torque is associated with the generation of spin and/or orbital angular momentum flow at the CGI. Spin-torque generation using a CGI expands the range of material choice for magnetic nonvolatile memory applications.","" "631% room temperature tunnel magnetoresistance with large oscillation effect in CoFe/MgO/CoFe(001) junctions","631% room temperature tunnel magnetoresistance with large oscillation effect in CoFe/MgO/CoFe(001) junctions","Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani","Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","122","11","112404","","2023-03-13","TRUE","","scientific_journal","eng","","10.1063/5.0145873","","We demonstrate tunnel magnetoresistance (TMR) ratios of up to 631% at room temperature (RT) using CoFe/MgO/CoFe(001) epitaxial magnetic tunnel junctions (MTJs). The TMR ratio increased up to 1143% at 10 K. The large TMR ratios resulted from the fine-tuning of the atomic-scale structures of the MTJs, such as crystallographic orientations and MgO interface oxidation, which are expected to enhance the well-known Δ1 coherent tunneling transport. Interestingly, the TMR oscillation effect, which is not covered by the standard coherent tunneling theory, also became significant. A 0.32-nm period TMR oscillation with increasing MgO thickness dominates the transport in a wide range of MgO thicknesses; the peak-to-valley difference of the TMR oscillation exceeds 140% at RT, which is attributed to the appearance of large oscillatory components in the resistance area product.","" "Elemental Doping and Interface Effects on Spin–Orbit Torques in CoSi‐Based Topological Semimetal Thin Films","Elemental Doping and Interface Effects on Spin–Orbit Torques in CoSi‐Based Topological Semimetal Thin Films","Ke Tang, Zhenchao Wen, Takeshi Seki, Hiroaki Sukegawa, Seiji Mitani","Ke Tang, Zhenchao Wen, Takeshi Seki, Hiroaki Sukegawa, Seiji Mitani","Advanced Materials Interfaces","Advanced Materials Interfaces","9","36","2201332","","2022-12-01","TRUE","","scientific_journal","eng","","10.1002/admi.202201332","","We report on Ni and Fe doping and interface effects on spin-orbit torques (SOTs) generated from a topological semimetal CoSi. CoSi thin films grown on Al2O3(0001) substrates by magnetron co-sputtering show the B20 structure with a texture in the [210] orientation even after Ni or Fe doping. The SOTs from the films exerted on the magnetization of a CoFeB layer are evaluated by harmonic Hall and spin-torque ferromagnetic resonance measurements. The spin Hall efficiency ξSH of the textured B20-CoSi at room temperature is determined to be 9.6%, which decreases to 1.8% for Ni0.15Co0.85Si and to 5.5% for Fe0.26Co0.74Si. The electrical conductivity dependence of the spin Hall conductivity is assigned to the regime of intrinsic mechanism of spin Hall effect, suggesting that the reduction of ξSH with the element doping could be due to the degradation in topological electronic structures of CoSi. Furthermore, inserting a Cu layer at the Co(Ni, Fe)Si/CoFeB interface resulted in an increase of the ξSH up to 10.9% for CoSi, 4.0% for Ni0.15Co0.85Si, and 8.3% for Fe0.26Co0.74Si. These enhancements of the ξSH could be attributed to the improvement in the interfacial spin transparency between the Co(Ni, Fe)Si and CoFeB layers.","" "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, Hiroaki Sukegawa, Kentaro Ogata, Gang Xiao, Hideo Kaiju","Kenta Sato, Hiroaki Sukegawa, Kentaro Ogata, Gang Xiao, Hideo Kaiju","Scientific Reports","Scientific Reports","12","1","","","2022-12-01","TRUE","","scientific_journal","eng","","10.1038/s41598-022-11545-6","","Magnetocapacitance (MC) effect has been observed in systems where both symmetries of time-reversal and space-inversion are broken, for examples, in multiferroic materials and spintronic devices. The effect has received increasing attention due to its interesting physics and the prospect of applications. Recently, a large tunnel magnetocapacitance (TMC) of 332% at room temperature was reported using MgO-based (001)-textured magnetic tunnel junctions (MTJs). Here, we report further enhancement in TMC beyond 420% at room temperature using epitaxial MTJs with an MgAl2O4(001) barrier with a cation-disordered spinel structure. This large TMC is partially caused by the high effective tunneling spin polarization, resulted from the excellent lattice matching between the Fe electrodes and the MgAl2O4 barrier. The epitaxial nature of this MTJ system sports an enhanced spin-dependent coherent tunneling effect. Among other factors leading to the large TMC are the appearance of the spin capacitance, the large barrier height, and the suppression of spin flipping through the MgAl2O4 barrier. We explain the observed TMC by the Debye-Fröhlich modelled calculation incorporating Zhang-sigmoid formula, parabolic barrier approximation, and spin-dependent drift diffusion model. Furthermore, we predict a 1000% TMC in MTJs with a spin polarization of 0.8. These experimental and theoretical findings provide a deeper understanding on the intrinsic mechanism of the TMC effect. New applications based on large TMC may become possible in spintronics, such as multi-value memories, spin logic devices, magnetic sensors, and neuromorphic computing.","" "Band-folding-driven high tunnel magnetoresistance ratios in (111)-oriented junctions with SrTiO3 barriers","Band-folding-driven high tunnel magnetoresistance ratios in (111)-oriented junctions with SrTiO3 barriers","Keisuke Masuda, Hiroyoshi Itoh, Yoshiaki Sonobe, Hiroaki Sukegawa, Seiji Mitani, Yoshio Miura","Keisuke Masuda, Hiroyoshi Itoh, Yoshiaki Sonobe, Hiroaki Sukegawa, Seiji Mitani, Yoshio Miura","Physical Review B","Physical Review B","106","13","","","2022-10-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.106.134438","","We theoretically study the tunnel magnetoresistance (TMR) effect in novel (111)-oriented magnetic tunnel junctions (MTJs) with SrTiO3 barriers, Co/SrTiO3/Co(111) and Ni/SrTiO3/Ni(111). Our analysis combining the first-principles calculation and the Landauer formula shows that the Co-based MTJ has a high TMR ratio over 500%, while the Ni-based MTJ has a smaller value (290%). Since the in-plane lattice periodicity of SrTiO3 is about twice as that of the primitive cell of fcc Co (Ni), the original bands of Co (Ni) are folded in the kx-ky plane corresponding to the ab-plane of the MTJ supercell. We find that this band folding gives a half-metallic band structure in the Lambda1 state of Co (Ni) and the coherent tunneling of such a half-metallic Lambda1 state yields a high TMR ratio. We also reveal that the difference in the TMR ratio between the Co- and Ni-based MTJs can be understood by different s-orbital weights in the Lambda1 band at the Fermi level.","" "Propagating backward-volume spin waves in epitaxial Fe films","Propagating backward-volume spin waves in epitaxial Fe films","S. Nezu, T. Scheike, H. Sukegawa, K. Sekiguchi","S. Nezu, T. Scheike, H. Sukegawa, K. Sekiguchi","AIP Advances","AIP Advances","12","3","035320","","2022-03-01","TRUE","","scientific_journal","eng","","10.1063/9.0000258","","The propagation characteristics of backward volume magnetostatic spin-waves in epitaxial Fe(001) films were studied by frequency-domain and time-domain spin-wave propagation spectroscopies using a vector network analyser. Due to the combination of cubic-magnetocrystalline anisotropy and anisotropic spin-wave dispersion, the backward volume spin-wave exhibited a complicated packet propagation. For the hard-axis propagation, the group velocity of the spin wave was greatly enhanced at low external magnetic fields and propagation occurred even under a no magnetic field. By analysing within a theoretical model and micromagnetic simulations, these transmission character of the backward volume magnetostatic spin-waves in an epitaxial iron film was well reproduced. The observed characteristics are essential information to promote two-dimensional magnonic devices utilizing cubic-anisotropic materials.","" "Enhanced tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","Enhanced tunnel magnetoresistance in Fe/Mg4Al-Ox/Fe(001) magnetic tunnel junctions","Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani","Thomas Scheike, Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","120","3","032404","","2022-01-17","TRUE","","scientific_journal","eng","","10.1063/5.0082715","","Spinel MgAl2O4 and family oxides are emerging barrier materials useful for magnetic tunnel junctions (MTJs). We report large tunnel magnetoresistance (TMR) ratios up to 429% at room temperature (RT) and 1034% at 10 K in a Fe/Mg-rich spinel/Fe(001) MTJ prepared using electron-beam evaporation of Mg4Al-Ox. Resistance oscillations with a MTJ barrier thickness of 0.3 nm were significantly enhanced compared to those of a Fe/MgO/Fe(001) MTJ, resulting in a large TMR oscillation peak-to-valley difference of 125% at RT. The differential conductance (dI/dV) spectra were symmetric with bias polarity, and the spectrum in the parallel magnetization state at low temperature demonstrates significant peaks within broad local minima at |V| = 0.2–0.6 V, indicating improved barrier interfaces by the Mg4Al-Ox barrier. This study demonstrates that TMR ratios in Fe(001)-MTJs can still be improved.","" "Heusler alloys for spintronic devices: review on recent development and future perspectives","Heusler alloys for spintronic devices: review on recent development and future perspectives","Kelvin Elphick, William Frost, Marjan Samiepour, Takahide Kubota, Koki Takanashi, Hiroaki Sukegawa, Seiji Mitani, Atsufumi Hirohata","Kelvin Elphick, William Frost, Marjan Samiepour, Takahide Kubota, Koki Takanashi, Hiroaki Sukegawa, Seiji Mitani, Atsufumi Hirohata","Science and Technology of Advanced Materials","Science and Technology of Advanced Materials","22","1","235","271","2021-12-31","TRUE","","scientific_journal","eng","","10.1080/14686996.2020.1812364","","Heusler alloys are theoretically predicted to become half-metals at room temperature (RT). The advantages of using these alloys are good lattice matching with major substrates, high Curie temperature above RT and intermetallic controllability for spin density of states at the Fermi energy level. The alloys are categorised into half- and full-Heusler alloys depending upon the crystalline structures, each being discussed both experimentally and theoretically. Fundamental properties of ferromagnetic Heusler alloys are described. Both structural and magnetic characterisations on an atomic scale are typically carried out in order to prove the half-metallicity at RT. Atomic ordering in the films is directly observed by X-ray diffraction and is also indirectly probed via the temperature dependence of electrical resistivity. Element specific magnetic moments and spin polarisation of the Heusler alloy films are directly measured using X-ray magnetic circular dichroism and Andreev reflection, respectively. By employing these ferromagnetic alloy films in a spintronic device, efficient spin injection into a non-magnetic material and large magnetoresistance are also discussed. Fundamental properties of antiferromagnetic Heusler alloys are then described. Both structural and magnetic characterisations on an atomic scale are shown. Atomic ordering in the Heusler alloy films is indirectly measured by the temperature dependence of electrical resistivity. Antiferromagnetic configurations are directly imaged by X-ray magnetic linear dichroism and polarised neutron reflection. The applications of the antiferromagnetic Heusler alloy films are also explained. The other nonmagnetic Heusler alloys are listed. A brief summary is provided at the end of this review.","" "Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite","Strain Engineering of Magnetic Anisotropy in Epitaxial Films of Cobalt Ferrite","Hiroshige Onoda, Hiroaki Sukegawa, Jun‐Ichiro Inoue, Hideto Yanagihara","Hiroshige Onoda, Hiroaki Sukegawa, Jun‐Ichiro Inoue, Hideto Yanagihara","Advanced Materials Interfaces","Advanced Materials Interfaces","8","23","2101034","","2021-12-01","TRUE","","scientific_journal","eng","","10.1002/admi.202101034","","Perpendicular magnetic anisotropy (PMA) energy up to Ku = 6.1+-0.8 MJm3 is demonstrated in this study by inducing large lattice-distortion exceeding 3% at room temperature in epitaxially distorted cobalt ferrite Co0.73Fe2.18O4(001) thin films. Although the thin film materials include no rare-earth elements or noble metals, the observed Ku is larger than that of the neodymium-iron boron compounds for high-performance permanent magnets. The large PMA is attributed to the significantly enhanced magnetoelastic effects, which are pronounced in distorted films with epitaxial lattice structures upon introducing a distortion control layer of composition Mg2-xSn1+xO4. Surprisingly, the induced Ku can be quantitatively explained in terms of the agreement between the local crystal field of Co2+ and the phenomenological magneto-elastic model, indicating that the linear response of induced Ku is sufficiently valid even under lattice distortions as large as 3.2%. Controlling tetragonal lattice deformation using a non-magnetic spinel layer for ferrites could be a promising protocol for developing materials with large magnetic anisotropies.","" "Spin Hall effect in a spin-1 chiral semimetal","Spin Hall effect in a spin-1 chiral semimetal","Ke Tang, Yong-Chang Lau, Kenji Nawa, Zhenchao Wen, Qingyi Xiang, Hiroaki Sukegawa, Takeshi Seki, Yoshio Miura, Koki Takanashi, Seiji Mitani","Ke Tang, Yong-Chang Lau, Kenji Nawa, Zhenchao Wen, Qingyi Xiang, Hiroaki Sukegawa, Takeshi Seki, Yoshio Miura, Koki Takanashi, Seiji Mitani","Physical Review Research","Physical Review Research","3","3","","","2021-07-01","TRUE","","scientific_journal","eng","","10.1103/physrevresearch.3.033101","","The spin-1 chiral semimetal is a state of quantum matter hosting unconventional chiral fermions that extend beyond the common Dirac and Weyl fermions. B20-type CoSi is a prototypal material that accommodates such an exotic quasiparticle. To date, the spin-transport properties in the spin-1 chiral semimetals have not been thoroughly explored. In this work, we fabricated B20-CoSi thin films on sapphire c-plane substrates by magnetron sputtering and studied the spin Hall effect (SHE) by combining experiments and first-principles calculations. The SHE of CoSi was investigated using CoSi/CoFeB/MgO heterostructures via spin Hall magnetoresistance and harmonic Hall measurements. First-principles calculations yield an intrinsic spin Hall conductivity (SHC) at the Fermi level that is consistent with the experiments and reveal its unique Fermi-energy dependence. Unlike the Dirac and Weyl fermion-mediated Hall conductivities that exhibit a peaklike structure centering around the topological node, SHC of B20-CoSi is odd and crosses zero at the node with two antisymmetric local extrema of opposite sign situated below and above in energy. Hybridization between Co d-Si p orbitals and spin-orbit coupling are essential for the SHC, despite the small (∼1%) weight of the Si p orbital near the Fermi level. This work expands the horizon of topological spintronics and highlights the importance of Fermi-level tuning in order to fully exploit the topology of spin-1 chiral fermions for spin-current generation.","" "Quantum-well tunneling anisotropic magnetoresistance above room temperature","Quantum-well tunneling anisotropic magnetoresistance above room temperature","Muftah Al-Mahdawi, Qingyi Xiang, Yoshio Miura, Mohamed Belmoubarik, Keisuke Masuda, Shinya Kasai, Hiroaki Sukegawa, Seiji Mitani","Muftah Al-Mahdawi, Qingyi Xiang, Yoshio Miura, Mohamed Belmoubarik, Keisuke Masuda, Shinya Kasai, Hiroaki Sukegawa, Seiji Mitani","Physical Review B","Physical Review B","103","18","","","2021-05-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.103.l180408","","Quantum-well (QW) devices have been extensively investigated in semiconductor structures. More recently, spin-polarized QWs were integrated into magnetic tunnel junctions (MTJs). In this Letter, we demonstrate the spin-based control of the quantized states in iron 3d-band QWs, as observed in experiments and theoretical calculations. We find that the magnetization rotation in the Fe QWs significantly shifts the QW quantization levels, which modulate the resonant-tunneling current in MTJs, resulting in a tunneling anisotropic magnetore- sistance (TAMR) effect of QWs. This QW-TAMR effect is sizable compared with other types of TAMR effect, and it is present above room temperature. In a QW MTJ of Cr/Fe/MgAl2O4/top electrode, where the QW is formed by a mismatch between Cr and Fe in the d band with 􏰀1 symmetry, a QW-TAMR ratio of up to 5.4% was observed at 5 K, which persisted to 1.2% even at 380 K. The magnetic control of QW transport can open new applications for spin-coupled optoelectronic devices, ultrathin sensors, and memory.","" "Magnetic, magnetoresistive and low-frequency noise properties of tunnel magnetoresistance sensor devices with amorphous CoFeBTa soft magnetic layers","Magnetic, magnetoresistive and low-frequency noise properties of tunnel magnetoresistance sensor devices with amorphous CoFeBTa soft magnetic layers","Mahmoud Rasly, Tomoya Nakatani, Jiangnan Li, Hossein Sepehri-Amin, Hiroaki Sukegawa, Yuya Sakuraba","Mahmoud Rasly, Tomoya Nakatani, Jiangnan Li, Hossein Sepehri-Amin, Hiroaki Sukegawa, Yuya Sakuraba","Journal of Physics D: Applied Physics","Journal of Physics D: Applied Physics","54","9","095002","","2021-03-04","TRUE","","scientific_journal","eng","","10.1088/1361-6463/abc2f5","","Magnetic field sensors using tunnel magnetoresistance (TMR) effect require linear resistance-magnetic field (R-H) response curves with small hysteresis, for which the soft magnetic property of the free layer (FL) is critical. In this work, we investigated amorphous CoFeBTa (CFBT) as a soft magnetic layer of the FL of CoFeB/MgO/CoFeB-based magnetic tunnel junctions in view of magnetic, TMR, and low-frequency noise properties. Two-step annealing process enabled an orthogonal magnetization configuration between FL and reference layer, by which linear R-H curve with small hysteresis were realized. The change of the R-H curve shape depending on the annealing temperature is explained by the Stoner- Wohlfarth model. The highest TMR ratio of ~160% and sensitivity of ~70 %/mT were obtained with a CFBT (20 nm)/Ta(0.3 nm)/CoFeB(3 nm) FL. The noise of the TMR devices are dominated by 1/f noise below ~10 kHz in frequency, which limits the ditectivity (D) of magnetic field by the sensor. The sensor devices patterned to 50 µm-diameter circular shapes showed a minimum D of ~2 nT/ √Hz at 10 Hz, which is superior to the previously reported values for TMR sensors with NiFe soft magnetic layers. ","" "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","Ke Tang, Zhenchao Wen, Yong-Chang Lau, Hiroaki Sukegawa, Takeshi Seki, Seiji Mitani","Ke Tang, Zhenchao Wen, Yong-Chang Lau, Hiroaki Sukegawa, Takeshi Seki, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","118","6","062402","","2021-02-08","TRUE","","scientific_journal","eng","","10.1063/5.0037178","","This study reports the magnetization switching induced by spin-orbit torque (SOT) from the spin current generated in Co2MnGa magnetic Weyl semimetal (WSM) thin films. We deposited epitaxial Co2MnGa thin films with highly B2-ordered structure on MgO(001) substrates. The SOT was characterized by harmonic Hall measurements in a Co2MnGa/Ti/CoFeB heterostructure and a relatively large spin Hall efficiency (ξSH) of −7.8% was obtained. The SOT-induced magnetization switching of the perpendicularly magnetized CoFeB layer was further demonstrated using the structure. The symmetry of second harmonic signals, thickness dependence of ξSH, and shift of anomalous Hall loops under applied currents were also investigated. This study not only contributes to the understanding of the mechanisms of spin-current generation from magnetic-WSM-based heterostructures, but also paves a way for the applications of magnetic WSMs in spintronic devices.","" "Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study","Interfacial giant tunnel magnetoresistance and bulk-induced large perpendicular magnetic anisotropy in (111)-oriented junctions with fcc ferromagnetic alloys: A first-principles study","Keisuke Masuda, Hiroyoshi Itoh, Yoshiaki Sonobe, Hiroaki Sukegawa, Seiji Mitani, Yoshio Miura","Keisuke Masuda, Hiroyoshi Itoh, Yoshiaki Sonobe, Hiroaki Sukegawa, Seiji Mitani, Yoshio Miura","Physical Review B","Physical Review B","103","6","","","2021-02-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.103.064427","","We study the tunnel magnetoresistance (TMR) effect and magnetocrystalline anisotropy in a series of magnetic tunnel junctions (MTJs) with L11-ordered fcc ferromagnetic alloys and MgO barrier along the [111] direction. Considering the (111)-oriented MTJs with different L11alloys, we calculate their TMR ratios and magnetocrystalline anisotropies on the basis of the first-principles calculations. The analysis shows that the MTJs with Co-based alloys (CoNi, CoPt, and CoPd) have high TMR ratios over 2000%. These MTJs have energetically favored Co-O interfaces where interfacial antibonding between Co d and O p states is formed around the Fermi level. We find that the resonant tunneling of the antibonding states, called the interface resonant tunneling, is the origin of the obtained high TMR ratios. Such a mechanism is similar to that found in our recent work on the simple Co/MgO/Co(111) MTJ [K. Masuda et al., Phys. Rev. B 101, 144404 (2020)]. In contrast, different systems have different spin channels where the interface resonant tunneling occurs; for example, the tunneling mainly occurs in the majority-spin channel in the CoNi-based MTJ while it occurs in the minority-spin channel in the CoPt-based MTJ. This means that even though the mechanism is similar, different spin channels contribute dominantly to the high TMR ratio in different systems. Such a difference is attributed to the different exchange splittings in the particular Co d states contributing to the tunneling though the antibonding with O p states. Our calculation of the magnetocrystalline anisotropy shows that many L11 alloys have large perpendicular magnetic anisotropy (PMA). In particular, CoPt has the largest value of anisotropy energy Ku≈10 MJ/m3. We further conduct a perturbation analysis of the PMA with respect to the spin-orbit interaction and reveal that the large PMA in CoPt and CoNi mainly originates from spin-conserving perturbation processes around the Fermi level.","" "Exceeding 400% tunnel magnetoresistance at room temperature in epitaxial Fe/MgO/Fe(001) spin-valve-type magnetic tunnel junctions","Exceeding 400% tunnel magnetoresistance at room temperature in epitaxial Fe/MgO/Fe(001) spin-valve-type magnetic tunnel junctions","Thomas Scheike, Qingyi Xiang, Zhenchao Wen, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Thomas Scheike, Qingyi Xiang, Zhenchao Wen, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","118","4","042411","","2021-01-25","TRUE","","scientific_journal","eng","","10.1063/5.0037972","","Giant tunnel magnetoresistance (TMR) ratios of 417% at room temperature (RT) and 914% at 3 K were demonstrated in epitaxial Fe/MgO/Fe(001) exchanged-biased spin-valve magnetic tunnel junctions (MTJs) by tuning growth conditions for each layer, combining sputter deposition for the Fe layers, electron-beam evaporation of the MgO barrier, and barrier interface tuning. Clear TMR oscillation as a function of the MgO thickness with a large peak-to-valley difference of ~80% was observed when the layers were grown on a highly (001)-oriented Cr buffer layer. Specific features of the observed MTJs are symmetric differential conductance (dI/dV) spectra for the bias polarity and plateau-like deep local minima in dI/dV (parallel configuration) at |V| = 0.2~0.5 V. At 3K, fine structures with two dips emerge in the plateau-like dI/dV, reflecting highly coherent tunneling through the Fe/MgO/Fe. We also observed a 496% TMR ratio at RT by a 2.24-nm-thick-CoFe insertion at the bottom-Fe/MgO interface.","" "Growth, strain, and spin-orbit torques in epitaxial Ni-Mn-Sb films sputtered on GaAs","Growth, strain, and spin-orbit torques in epitaxial Ni-Mn-Sb films sputtered on GaAs","N. Zhao, A. Sud, H. Sukegawa, S. Komori, K. Rogdakis, K. Yamanoi, J. Patchett, J. W. A. Robinson, C. Ciccarelli, H. Kurebayashi","N. Zhao, A. Sud, H. Sukegawa, S. Komori, K. Rogdakis, K. Yamanoi, J. Patchett, J. W. A. Robinson, C. Ciccarelli, H. Kurebayashi","Physical Review Materials","Physical Review Materials","5","1","","","2021-01-01","TRUE","","scientific_journal","eng","","10.1103/physrevmaterials.5.014413","","We report current-induced spin torques in epitaxial NiMnSb films on a commercially available epi-ready GaAs substrate. The NiMnSb was grown by co-sputtering from three targets using optimised parameter. The films were processed into micro-scale bars to perform current-induced spin-torque measurements. Magnetic dynamics were excited by microwave currents and electric voltages along the bars were measured to analyse the symmetry of the current-induced torques. We found that the extracted symmetry of the spin torques matches those expected from spin-orbit interaction in a tetragonally distorted half-Heusler crystal. Both field-like and damping-like torques are observed in all the samples characterised, and the efficiency of the current-induced torques is comparable to that of ferromagnetic metal/heavy metal bilayers.","" "Study of Induced Magnetic Anisotropy by Lattice Distortion in Cobalt Ferrite Thin Film Grown on (Mg,Sn)3O4 Buffer Layers","Study of Induced Magnetic Anisotropy by Lattice Distortion in Cobalt Ferrite Thin Film Grown on (Mg,Sn)3O4 Buffer Layers","H. Onoda, H. Sukegawa, H. Yanagihara","H. Onoda, H. Sukegawa, H. Yanagihara","IEEE Transactions on Magnetics","IEEE Transactions on Magnetics","56","3","1","4","2020","TRUE","","scientific_journal","eng","","10.1109/tmag.2019.2962025","","We have investigated structural and magnetic properties of cobalt ferrite (CFO)(001) epitaxial thin films grown by RF magnetron sputtering method on (Mg,Sn)3O4 (MSO) buffer layers to induce large perpendicular magnetic anisotropy (PMA) through the magneto-elastic effect. Tuning of the CFO distortion was demonstrated by changing the film thickness of CFO. Torque measurements revealed that a 5-nm thick CFO thin film showed the PMA constant Ku = 25.8 ± 1.3 Merg/cm3 at room temperature, which is extraordinarily large for a ferromagnetic oxide.","" "Spin-Resolved Contribution to Perpendicular Magnetic Anisotropy and Gilbert Damping in Interface-Engineered Fe/MgAl2O4 Heterostructures","Spin-Resolved Contribution to Perpendicular Magnetic Anisotropy and Gilbert Damping in Interface-Engineered Fe/MgAl2O4 Heterostructures","Ruma Mandal, Qingyi Xiang, Keisuke Masuda, Yoshio Miura, Hiroaki Sukegawa, Seiji Mitani, Yukiko K. Takahashi","Ruma Mandal, Qingyi Xiang, Keisuke Masuda, Yoshio Miura, Hiroaki Sukegawa, Seiji Mitani, Yukiko K. Takahashi","Physical Review Applied","Physical Review Applied","14","6","","","2020-12-01","TRUE","","scientific_journal","eng","","10.1103/physrevapplied.14.064027","","The coexistence of a low magnetic Gilbert damping constant and large perpendicular magnetic anisotropy (PMA) in ferromagnetic thin films is critical for high-speed and energy-efficient spintronics devices. To clarify the spin-resolved contributions of damping and PMA, a flat, lattice-matched interface is developed in an Fe(0.7 nm)/MgAl2O4(oxide)(3 nm) bi-layer film by varying the ex situ annealing temperature, which acts as a catalyst to vary the PMA energy densities according to the oxidation degree. Here, the optimized procedure for interface engineering is implemented to achieve an extremely low magnetic Gilbert damping constant (0.013) and a strong interfacial PMA energy (0.8MJm−3) for epitaxial thin films. By employing different interfacial atomic configurations in a first-principles calculation, this study explains the origin of the PMA energy and damping constant. The d(yz) and d(zx) orbitals of the interfacial Fe atoms in the minority-spin states play a role in the orbital moment and its anisotropy. Furthermore, the matrix elements between these two orbitals in the non-spin-flip term predominately contribute to damping. These detailed findings provide a clear insight into the development of materials with significantly improved PMA energies and low damping characteristics, thereby facilitating promising future spintronic applications.","" "Controlling oxygen distribution of an MgAl2O4 barrier for magnetic tunnel junctions by two-step process","Controlling oxygen distribution of an MgAl2O4 barrier for magnetic tunnel junctions by two-step process","Shinto Ichikawa, P.-H. Cheng, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani, Katsuyuki Nakada","Shinto Ichikawa, P.-H. Cheng, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani, Katsuyuki Nakada","Applied Physics Letters","Applied Physics Letters","117","12","122409","","2020-09-21","TRUE","","scientific_journal","eng","","10.1063/5.0015474","","A MgAl2O4 barrier with an ordered spinel structure for magnetic tunnel junctions (MTJs) was prepared via a two-step process by repeating the Mg–Al alloy deposition and post-oxidation to tune its oxidation state. The as-obtained Fe/MgAl2O4/Fe(001) epitaxial MTJs showed a large tunnel magnetoresistance (TMR) ratio (>150%) in a wide resistance x area (RA) range; this behavior was in contrast with that of MTJs prepared through a conventional one-step process, which exhibited a large TMR ratio only in a narrow RA range. The bias voltage at which the TMR is halved from the zero-bias value increased up to 1.20 and 1.47 V for the positive and negative bias polarities, respectively, when optimizing the two-step process. The nanostructure analysis revealed an improved oxygen distribution on the atomic scale in the MgAl2O4 barrier with the two-step process, providing a coherent barrier suitable for various practical applications. ","" "Effect of tungsten doping on perpendicular magnetic anisotropy and its voltage effect in single crystal Fe/MgO(0 0 1) interfaces","Effect of tungsten doping on perpendicular magnetic anisotropy and its voltage effect in single crystal Fe/MgO(0 0 1) interfaces","Yuki Iida, Qingyi Xiang, Jun Okabayashi, Thomas Scheike, Hiroaki Sukegawa, Seiji Mitani","Yuki Iida, Qingyi Xiang, Jun Okabayashi, Thomas Scheike, Hiroaki Sukegawa, Seiji Mitani","Journal of Physics D: Applied Physics","Journal of Physics D: Applied Physics","53","12","124001","","2020-03-18","TRUE","","scientific_journal","eng","","10.1088/1361-6463/ab5c93","","Heavy metal elements with strong spin–orbit coupling generally play an important role for perpendicular magnetic anisotropy (PMA) in magnetic heterostructures. We examined interface PMA and related properties in single crystal Fe/MgO(0 0 1) heterostructures in which a very thin W interface layer was nominally inserted as doping. The PMA energy density was reduced with increasing the W layer thickness, in contrast to the results in a similar study using poly-crystal FeB/MgO heterostructures (Nozaki et al 2018 APL Mater. 6 026101), suggesting that the detailed mechanisms of PMA are different between single crystal Fe/MgO and poly-crystal FeB/MgO. X-ray magnetic circular dichroism measurements revealed that anisotropy in the Fe orbital magnetic moments decreased with the PMA energy density, i.e. the PMA observed was interpreted in the framework of Bruno’s model (Bruno 1989 Phys. Rev. B 39 R865). The coefficient of the voltage effect of PMA arising in the Fe/MgO heterostructure with 0.05 nm thick W interface insertion was determined to be ~190 fJ Vm−1, showing a small quantity of reduction as well as the PMA. This study gives an insight into the role of heavy metal elements in the PMA for single crystal Fe/MgO heterostructures.","" "Comparative study of spin-dependent transport in Co2FeAl/MgAl2O4/CoFe magnetic tunnel junctions with and without thin CoFe interface insertion: an elastic and inelastic scattering model analysis","Comparative study of spin-dependent transport in Co2FeAl/MgAl2O4/CoFe magnetic tunnel junctions with and without thin CoFe interface insertion: an elastic and inelastic scattering model analysis","Thomas Scheike, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Thomas Scheike, Hiroaki Sukegawa, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Journal of Physics D: Applied Physics","Journal of Physics D: Applied Physics","53","4","045001","","2020-01-23","TRUE","","scientific_journal","eng","","10.1088/1361-6463/ab50d0","","Co2FeAl/MgAlO/CoFeトンネル接合における、CoFe層挿入の有無による構造とトンネル伝導の違いを調べた。まず、バリア層の厚さに違いがなくても、トンネル抵抗が大きく異なることを確認した。続いて、モデル解析により、CoFe層挿入によって抵抗が急激に低下し、さらにその温度係数が正になる現象は、弾性的トンネル過程が支配的になることで説明できた。","" "Perpendicular orbital and quadrupole anisotropies at Fe/MgO interfaces detected by x-ray magnetic circular and linear dichroisms","Perpendicular orbital and quadrupole anisotropies at Fe/MgO interfaces detected by x-ray magnetic circular and linear dichroisms","Jun Okabayashi, Yuki Iida, Qingyi Xiang, Hiroaki Sukegawa, Seiji Mitani","Jun Okabayashi, Yuki Iida, Qingyi Xiang, Hiroaki Sukegawa, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","115","25","252402","","2019-12-16","TRUE","","scientific_journal","eng","","10.1063/1.5127665","","We investigated interfacial perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO(001) using both x-ray magnetic circular dichroism and magnetic linear dichroism (XMLD). We developed the XMLD technique for detecting the signals from the PMA samples. The PMA energy and quadrupole moments at an Fe/MgO interface were deduced from the XMLD sum rules, whose values explain the microscopic origin of PMA. We found that orbital moment anisotropy is dominant at the Fe/MgO interfacial PMA and the contribution of quadrupole moments is small but finite at the lattice distorted interfaces.","" "Realizing Room‐Temperature Resonant Tunnel Magnetoresistance in Cr/Fe/MgAl 2 O 4 Quasi‐Quantum Well Structures","Realizing Room‐Temperature Resonant Tunnel Magnetoresistance in Cr/Fe/MgAl 2 O 4 Quasi‐Quantum Well Structures","Qingyi Xiang, Hiroaki Sukegawa, Mohamed Belmoubarik, Muftah Al‐Mahdawi, Thomas Scheike, Shinya Kasai, Yoshio Miura, Seiji Mitani","Qingyi Xiang, Hiroaki Sukegawa, Mohamed Belmoubarik, Muftah Al‐Mahdawi, Thomas Scheike, Shinya Kasai, Yoshio Miura, Seiji Mitani","Advanced Science","Advanced Science","6","20","1901438","","2019-10-01","TRUE","","scientific_journal","eng","","10.1002/advs.201901438","","格子整合性に優れ、原子層を正確に制御したCr/Fe/MgAlO擬量子井戸構造を創製し、室温での明瞭な共鳴トンネル効果とトンネル磁気抵抗効果の増大現象を実証した。トンネル抵抗の特異な温度依存性の測定において、トンネル磁気抵抗効果に寄与する量子井戸準位がFeのデルタ1状態であることを(理論解析ではなく)実験的に示唆する結果を得た。","" "Towards Oxide Electronics: a Roadmap","Towards Oxide Electronics: a Roadmap","M. Coll, J. Fontcuberta, M. Althammer, M. Bibes, H. Boschker, A. Calleja, G. Cheng, M. Cuoco, R. Dittmann, B. Dkhil, I. El Baggari, M. Fanciulli, I. Fina, E. Fortunato, C. Frontera, S. Fujita, V. Garcia, S.T.B. Goennenwein, C.-G. Granqvist, J. Grollier, R. Gross, A. Hagfeldt, G. Herranz, K. Hono, E. Houwman, M. Huijben, A. Kalaboukhov, D.J. Keeble, G. Koster, L.F. Kourkoutis, J. Levy, M. Lira-Cantu, J.L. MacManus-Driscoll, Jochen Mannhart, R. Martins, S. Menzel, T. Mikolajick, M. Napari, M.D. Nguyen, G. Niklasson, C. Paillard, S. Panigrahi, G. Rijnders, F. Sánchez, P. Sanchis, S. Sanna, D.G. Schlom, U. Schroeder, K.M. Shen, A. Siemon, M. Spreitzer, H. Sukegawa, R. Tamayo, J. van den Brink, N. Pryds, F. Miletto Granozio","M. Coll, J. Fontcuberta, M. Althammer, M. Bibes, H. Boschker, A. Calleja, G. Cheng, M. Cuoco, R. Dittmann, B. Dkhil, I. El Baggari, M. Fanciulli, I. Fina, E. Fortunato, C. Frontera, S. Fujita, V. Garcia, S.T.B. Goennenwein, C.-G. Granqvist, J. Grollier, R. Gross, A. Hagfeldt, G. Herranz, K. Hono, E. Houwman, M. Huijben, A. Kalaboukhov, D.J. Keeble, G. Koster, L.F. Kourkoutis, J. Levy, M. Lira-Cantu, J.L. MacManus-Driscoll, Jochen Mannhart, R. Martins, S. Menzel, T. Mikolajick, M. Napari, M.D. Nguyen, G. Niklasson, C. Paillard, S. Panigrahi, G. Rijnders, F. Sánchez, P. Sanchis, S. Sanna, D.G. Schlom, U. Schroeder, K.M. Shen, A. Siemon, M. Spreitzer, H. Sukegawa, R. Tamayo, J. van den Brink, N. Pryds, F. Miletto Granozio","Applied Surface Science","Applied Surface Science","482","","1","93","2019-07-01","TRUE","","scientific_journal","eng","","10.1016/j.apsusc.2019.03.312","","Oxide science and technology has been the target of a wide four-year project, named Towards Oxide-Based Electronics (TO-BE), that has been recently running in Europe and has involved as participants several hundred scientists from 29 EU countries. In this review and perspective paper, published as a final deliverable of the TO-BE Action, the opportunities of oxides as future electronic materials for Information and Communication Technologies ICT and Energy are discussed. The paper is organized as a set of contributions, all selected and ordered as individual building blocks of a wider general scheme. After a brief preface by the editors and an introductory contribution, two sections follow. The first is mainly devoted to providing a perspective on the latest theoretical and experimental methods that are employed to investigate oxides and to produce oxide-based films, heterostructures and devices. In the second, all contributions are dedicated to different specific fields of applications of oxide thin films and heterostructures, in sectors as data storage and computing, optics and plasmonics, magnonics, energy conversion and harvesting, and power electronics.","" "Control of Magnetic Anisotropy by Lattice Distortion in Cobalt Ferrite Thin Film","Control of Magnetic Anisotropy by Lattice Distortion in Cobalt Ferrite Thin Film","H. Onoda, H. Sukegawa, E. Kita, H. Yanagihara","H. Onoda, H. Sukegawa, E. Kita, H. Yanagihara","IEEE Transactions on Magnetics","IEEE Transactions on Magnetics","54","11","1","4","2018","TRUE","","scientific_journal","eng","","10.1109/tmag.2018.2833880","","We have investigated the properties of cobalt ferrite (CFO)(001) epitaxial thin films grown by RF magnetron sputtering method on various buffer layers to induce large perpendicular magnetic anisotropy (PMA) through the magneto-elastic effect. Among five different compounds examined as the buffer layers, we found that only CFO thin films grown on (Mg, Sn)3O4 buffer layers showed a strong PMA, and the value of the saturation magnetization was 460 emu/cm3, which is larger than the 425 emu/cm3 for bulk CFO. Torque measurements revealed the PMA energy Ku = 24.6 Merg/cm3 at room temperature, which is extraordinarily large for a ferromagnetic oxide.","" "Optical and Magnetic Properties of Fluorescent Ammonium Silicon Fluoride Microparticles with Magnetic Function","磁性機能を付加した蛍光性 (NH4)2SiF6微粒子の光学および磁気特性","工藤 賢哉, 佐藤 慶介, 介川 裕章, 平栗 健二","工藤 賢哉, 佐藤 慶介, 介川 裕章, 平栗 健二","照明学会誌","照明学会誌","102","6","215","219","2018","TRUE","","scientific_journal","jpn","","10.2150/jieij.170000566","","","Magneto-fluorescent microparticles have gained attention as novel biomedical materials because they can provide simultaneously the diagnostic trace of disease site by fluorescence imaging and their hyperthermia therapy by magnetic materials. In the design of such microparticles, the reduction in production cost and the simplification of manufacturing process are absolutely critical. The simplified procedure to synthesize magneto-fluorescent microparticles combining fluorescent ammonium silicon fluoride ((NH4)2SiF6) and magnetic iron oxides (Fe3O4) have been investigated. Moreover, we have also discussed the magnetic and fluorescent behaviors of the microparticles." "Large perpendicular magnetic anisotropy in epitaxial Fe/MgAl2O4(001) heterostructures","Large perpendicular magnetic anisotropy in epitaxial Fe/MgAl2O4(001) heterostructures","Qingyi Xiang, Ruma Mandal, Hiroaki Sukegawa, Yukiko K. Takahashi, Seiji Mitani","Qingyi Xiang, Ruma Mandal, Hiroaki Sukegawa, Yukiko K. Takahashi, Seiji Mitani","Applied Physics Express","Applied Physics Express","11","6","063008","","2018-06-01","TRUE","","scientific_journal","eng","","10.7567/apex.11.063008","","We investigated the perpendicular magnetic anisotropy (PMA) and related properties of epitaxial Fe (0.7 nm)/MgAl2O4(001) heterostructures prepared by electron beam evaporation. Using an optimized structure, we obtained a large PMA energy of >1MJ/m3 at room temperature, which is comparable to that in ultrathin-Fe/MgO(001) heterostructures. Both the PMA energy and saturation magnetization showed a weak temperature dependence, ensuring a wide working temperature range in applications. The effective magnetic damping constant of the 0.7nm Fe layer was found to be >0.02 using the time-resolved magneto-optical Kerr effect. This study demonstrated the suitability of the Fe/MgAl2O4 heterostructure for use in perpendicular magnetic tunnel junctions, as well as good agreement with theoretical predictions.","" "Microstructural evolution of perpendicular magnetization films with an ultra-thin Co2FeAl/MgAl2O4(001) structure","Microstructural evolution of perpendicular magnetization films with an ultra-thin Co2FeAl/MgAl2O4(001) structure","Jason Paul Hadorn, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Jason Paul Hadorn, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Acta Materialia","Acta Materialia","145","","306","315","2018-02-01","TRUE","","scientific_journal","eng","","10.1016/j.actamat.2017.12.018",""," スピネル(MgAl2O4)/Co2FeAl超薄膜界面に誘起される垂直磁気異方性のメカニズムをSTEMイメージングに基づいて検討した。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酸化とポスト加熱処理によって実現するとともに界面近傍のAl拡散が強い磁気異方性の起源を担っていることを明らかにした。","" "Giant tunnel magnetoresistance in polycrystalline magnetic tunnel junctions with highly textured MgAl2O4(001) based barriers","Giant tunnel magnetoresistance in polycrystalline magnetic tunnel junctions with highly textured MgAl2O4(001) based barriers"," Ikhtiar, Hiroaki Sukegawa, Xiandong Xu, Mohamed Belmoubarik, Hwachol Lee, Shinya Kasai, Kazuhiro Hono"," Ikhtiar, Hiroaki Sukegawa, Xiandong Xu, Mohamed Belmoubarik, Hwachol Lee, Shinya Kasai, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","112","2","022408","","2018-01-08","TRUE","","scientific_journal","eng","","10.1063/1.5013076","","In this work, we demonstrate the growth of polycrystalline-based MTJs with large TMR ratios exceeding 240% and improved bias voltage dependence compared to that of MgO-based MTJs. An ultra-thin CoFe/MgO seed layer on amorphous CoFeB layer induced the growth of a highly (001)-textured MgAl2O4 barrier, which worked as a template layer for the solid epitaxy of CoFe grains during the crystallization of the CoFeB layers. High resolution scanning transmission electron microscopy shows lattice-matched epitaxy between the (001)-textured MgAl2O4 barrier and CoFe grains. This study demonstrates the industrial viability of MgAl2O4-based polycrystalline MTJs with improved bias voltage dependence.","" "Investigation of ramped voltage stress to screen defective magnetic tunnel junctions","Investigation of ramped voltage stress to screen defective magnetic tunnel junctions","Chulmin Choi, Hiroaki Sukegawa, Seiji Mitani, Yunheub Song","Chulmin Choi, Hiroaki Sukegawa, Seiji Mitani, Yunheub Song","Semiconductor Science and Technology","Semiconductor Science and Technology","33","1","015006","","2018-01-01","TRUE","","scientific_journal","eng","","10.1088/1361-6641/aa99bb","","A ramped voltage stress method to screen defective magnetic tunnel junctions (MTJs) is investigated in order to improve screen accuracy and shorten test time. Approximately 1500 MTJs with 1.25 nm thick tunnel barriers were fabricated for this evaluation, and normal MTJs show a 189 % tunnel magnetoresistance ratio, a 365 Ω·μm2 resistance-area product, and a 1.8 V breakdown voltage, which is enough for applying reliable screen tests. We successfully classified MTJs as normal MTJs having good characteristics or defective MTJs having insufficient endurance and showing resistance degradation after only short-term cycling. Using the ramped voltage stress screen test with slow ramp speed, it is demonstrated that remarkable screening performance and little dependence on temperature are obta","" "Voltage control of magnetic anisotropy in epitaxial Ru/Co2FeAl/MgO heterostructures","Voltage control of magnetic anisotropy in epitaxial Ru/Co2FeAl/MgO heterostructures","Zhenchao Wen, Hiroaki Sukegawa, Takeshi Seki, Takahide Kubota, Koki Takanashi, Seiji Mitani","Zhenchao Wen, Hiroaki Sukegawa, Takeshi Seki, Takahide Kubota, Koki Takanashi, Seiji Mitani","Scientific Reports","Scientific Reports","7","1","","","2017-12-01","TRUE","","scientific_journal","eng","","10.1038/srep45026","","Voltage control of magnetic anisotropy (VCMA) in magnetic heterostructures is a key technology for achieving energy-efficiency electronic devices with ultralow power consumption. Here, we report the first demonstration of the VCMA effect in novel epitaxial Ru/Co2FeAl(CFA)/MgO heterostructures with interfacial perpendicular magnetic anisotropy (PMA). Perpendicularly magnetized tunnel junctions with the structure of Ru/CFA/MgO were fabricated and exhibited an effective voltage control on switching fields for the CFA free layer. Large VCMA coefficients of 108 and 139 fJ/Vm for the CFA film were achieved at room temperature and 4 K, respectively. The interfacial stability in the heterostructure was confirmed by repeating measurements.","" "Nonlinear electric field effect on perpendicular magnetic anisotropy in Fe/MgO interfaces","Nonlinear electric field effect on perpendicular magnetic anisotropy in Fe/MgO interfaces","Qingyi Xiang, Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Takeshi Seki, Takahide Kubota, Koki Takanashi, Seiji Mitani","Qingyi Xiang, Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Takeshi Seki, Takahide Kubota, Koki Takanashi, Seiji Mitani","Journal of Physics D: Applied Physics","Journal of Physics D: Applied Physics","50","40","40LT04","","2017-10-11","TRUE","","scientific_journal","eng","","10.1088/1361-6463/aa87ab","","The electric field effect on magnetic anisotropy was studied in an ultrathin Fe(001) monocrystalline layer sandwiched between Cr buffer and MgO tunnel barrier layers, mainly through post-annealing temperature and measurement temperature dependences. A large coefficient of the electric field effect of more than 200 fJ (Vm)−1 was observed in the negative range of electric field, as well as an areal energy density of perpendicular magnetic anisotropy (PMA) of around 600 μJ m−2. More interestingly, nonlinear behavior, giving rise to a local minimum around +100 mV nm−1, was observed in the electric field dependence of magnetic anisotropy, being independent of the post-annealing and measurement temperatures. The insensitivity to both the interface conditions and the temperature of the system","" "TDDB modeling depending on interfacial conditions in magnetic tunnel junctions","TDDB modeling depending on interfacial conditions in magnetic tunnel junctions","Chul-Min Choi, Hiroaki Sukegawa, Seiji Mitani, Yun-Heub Song","Chul-Min Choi, Hiroaki Sukegawa, Seiji Mitani, Yun-Heub Song","Semiconductor Science and Technology","Semiconductor Science and Technology","32","10","105007","","2017-10-01","TRUE","","scientific_journal","eng","","10.1088/1361-6641/aa856e","","We investigated time-dependent dielectric breakdown (TDDB) modeling for MgO dielectrics with/without Mg insertion of MgO-based magnetic tunnel junctions (MTJs). The number of permanent trap sites at the no-Mg insertion interface was much larger than that at the Mg-inserted interface as determined by interval voltage stress (IVS) tests. The interfacial conditions related to trap sites at MgO dielectrics give rise to the different TDDB modeling. Here, we confirmed that the TDDB curves obtained from the constant voltage stress (CVS) tests for the Mg inserted interface case were well fitted by the power-law voltage V model, while the case of no-Mg inserted interface showed a good correlation to the 1/E model. The difference in the TDDB models related to interfacial conditions was understood ba","" " Endurance of magnetic tunnel junctions under dynamic voltage stress "," Endurance of magnetic tunnel junctions under dynamic voltage stress ","C.M. Choi, H. Sukegawa, S. Mitani, Y.H. Song","C.M. Choi, H. Sukegawa, S. Mitani, Y.H. Song"," Electronics Letters"," Electronics Letters","53","16","1146","1148","2017-08-03","TRUE","","scientific_journal","eng","","10.1049/el.2017.1579","","MgAl2O4 (MAO)-based magnetic tunnel junctions (MTJs) with an MAO thickness of ∼1.25 nm are fabricated and their cycling characteristics under dynamic voltage stress are evaluated. The speed of breakdown strongly depended on the pulse polarities used, bipolar, positive unipolar, and negative unipolar. The bipolar condition yielded more rapid breakdown under cycling. Between the two unipolar conditions, positive bias yielded more rapid breakdown than negative bias; the difference between these is understood to arise from the conditions of the interface between the MAO and ferromagnetic layers. Among apparently normal MTJ cells showing little resistance drift,20% were degraded during a long cycling test in the bipolar stress condition. Thus, the use of bipolar voltage stress i","" "Spin-wave propagation in cubic anisotropic materials","Spin-wave propagation in cubic anisotropic materials","Koji Sekiguchi, Seo-Won Lee, Hiroaki Sukegawa, Nana Sato, Se-Hyeok Oh, Robert D McMichael, Kyung-Jin Lee","Koji Sekiguchi, Seo-Won Lee, Hiroaki Sukegawa, Nana Sato, Se-Hyeok Oh, Robert D McMichael, Kyung-Jin Lee","NPG Asia Materials","NPG Asia Materials","9","6","e392","","2017-06-30","TRUE","","scientific_journal","eng","","10.1038/am.2017.87","","The information carrier of modern technologies is the electron charge, whose transport inevitably generates Joule heating. Spin waves, the collective precessional motion of electron spins, do not involve moving charges and thus avoid Joule heating. In this respect, magnonic devices in which the information is carried by spin waves attract interest for low-power computing. However, implementation of magnonic devices for practical use suffers from a low spin-wave signal and on/off ratio. Here, we demonstrate that cubic anisotropic materials can enhance spin-wave signals by improving spin-wave amplitude as well as group velocity and attenuation length. Furthermore, cubic anisotropic materials show an enhanced on/off ratio through a laterally localized edge mode, which closely mimics the gate-","" "Increased magnetic damping in ultrathin films of Co2FeAl with perpendicular anisotropy","Increased magnetic damping in ultrathin films of Co2FeAl with perpendicular anisotropy","Y. K. Takahashi, Y. Miura, R. Choi, T. Ohkubo, Z. C. Wen, K. Ishioka, R. Mandal, R. Medapalli, H. Sukegawa, S. Mitani, E. E. Fullerton, K. Hono","Y. K. Takahashi, Y. Miura, R. Choi, T. Ohkubo, Z. C. Wen, K. Ishioka, R. Mandal, R. Medapalli, H. Sukegawa, S. Mitani, E. E. Fullerton, K. Hono","Applied Physics Letters","Applied Physics Letters","110","25","252409","","2017-06-19","TRUE","","scientific_journal","eng","","10.1063/1.4989379","","We estimated the magnetic damping constant a of Co2FeAl (CFA) Heusler alloy films of differentthicknesses with an MgO capping layer by means of time-resolved magneto-optical Kerr effect andferromagnetic resonance measurements. CFA films with thicknesses of 1.2 nm and below exhibitedperpendicular magnetic anisotropy arising from the presence of the interface with MgO. Whilea 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-principles calculations, we attributed the origin of the large a in the ultrathin CFA film primarily to the Al deficiency in the CFA layer, which caused an increase in the density of states and thereby in the scatterings","" "Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited MgAl2O4/Fe(001) magnetic tunnel junctions","Effect of Mg-Al insertion on magnetotransport properties in epitaxial Fe/sputter-deposited MgAl2O4/Fe(001) magnetic tunnel junctions","Mohamed Belmoubarik, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Mohamed Belmoubarik, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","AIP Advances","AIP Advances","7","5","055908","","2017-05-01","TRUE","","scientific_journal","eng","","10.1063/1.4973393","","We investigated the effect of an Mg-Al layer insertion at the bottom interface of epitaxial Fe/MgAl2O4/Fe(001) magnetic tunnel junctions (MTJs) on their spin-dependent transport properties. The tunnel magnetoresistance (TMR) ratio and differential conductance spectra for the parallel magnetic configuration exhibited clear dependence on the inserted Mg-Al thickness. A slight Mg-Al insertion (thickness < 0.1 nm) was effective for obtaining a large TMR ratio above 200% at room temperature and observing a distinct local minimum structure in conductance spectra. In contrast, thicker Mg-Al (> 0.2 nm) induced a reduction of TMR ratios and featureless conductance spectra, indicating a degradation of the bottom-Fe/MgAl2O4 interface. Therefore, a minimal Mg-Al insertion was found to be effecti","" "Time-dependent dielectric breakdown of MgO magnetic tunnel junctions and novel test method","REGULAR PAPERS Time-dependent dielectric breakdown of MgO magnetic tunnel junctions and novel test method","Kyungjun Kim, Chulmin Choi, Youngtaek Oh, Hiroaki Sukegawa, Seiji Mitani, Yunheub Song","Kyungjun Kim, Chulmin Choi, Youngtaek Oh, Hiroaki Sukegawa, Seiji Mitani, Yunheub Song","Japanese Journal of Applied Physics","Japanese Journal of Applied Physics","56","4S","04CN02","","2017-04-01","TRUE","","scientific_journal","eng","","10.7567/jjap.56.04cn02","","Time-dependent dielectric breakdown (TDDB), which is used to measure reliability, depends on both the thickness of the tunnel barrier and bias voltage. In addition, the heat generated by self-heating in a magnetic tunneling junction (MTJ) affects TDDB. Therefore, we investigated TDDB with the self-heating effect for a MgO tunnel barrier with thicknesses of 1.1 and 1.2nm by the constant voltage stress (CVS) method. Using the results of this experiment, we predicted a TDDB of 1.0nm for the tunnel barrier. Also, we suggested the use of not only the CVS method, which is a common way of determining TDDB, but also the constant current stress (CCS) method, which compensates for the disadvantages of the CVS method.","" "MgGa2O4 spinel barrier for magnetic tunnel junctions: Coherent tunneling and low barrier height","MgGa2O4 spinel barrier for magnetic tunnel junctions: Coherent tunneling and low barrier height","Hiroaki Sukegawa, Yushi Kato, Mohamed Belmoubarik, P.-H. Cheng, Tadaomi Daibou, Naoharu Shimomura, Yuuzo Kamiguchi, Junichi Ito, Hiroaki Yoda, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Hiroaki Sukegawa, Yushi Kato, Mohamed Belmoubarik, P.-H. Cheng, Tadaomi Daibou, Naoharu Shimomura, Yuuzo Kamiguchi, Junichi Ito, Hiroaki Yoda, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","110","12","122404","","2017-03-20","TRUE","","scientific_journal","eng","","10.1063/1.4977946","","Epitaxial Fe/magnesium gallium spinel oxide (MgGa2O4)/Fe(001) magnetic tunnel junctions (MTJs) were fabricated by magnetron sputtering. A tunnel magnetoresistance (TMR) ratio up to 121% at room temperature (196% at 4K) was observed, suggesting a TMR enhancement by the coherent tunneling effect in the MgGa2O4 barrier. The MgGa2O4 layer had a spinel structure and it showed good lattice matching with the Fe layers owing to slight tetragonal lattice distortion of MgGa2O4. Barrier thickness dependence of the tunneling resistance and current-voltage characteristics revealed that the height of the MgGa2O4 barrier is much lower than that of an MgAl2O4 barrier. This study demonstrates the potential of Ga-based spinel oxides for MTJ barriers having a large TMR ratio at a low resistance area product.","" "Perpendicular magnetic anisotropy at lattice-matched Co2FeAl/MgAl2O4(001) epitaxial interfaces","Perpendicular magnetic anisotropy at lattice-matched Co2FeAl/MgAl2O4(001) epitaxial interfaces","Hiroaki Sukegawa, Jason Paul Hadorn, Zhenchao Wen, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Hiroaki Sukegawa, Jason Paul Hadorn, Zhenchao Wen, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","110","11","112403","","2017-03-13","TRUE","","scientific_journal","eng","","10.1063/1.4978663","","We report perpendicular magnetic anisotropy (PMA) induced at Co2FeAl/MgAl2O4(001) epitaxial interfaces prepared by magnetron sputtering and post-oxidation of MgAl layers. A PMA energy density of more than 4 Merg/cm3 for 1-nm-thick Co2FeAl layers and an effective interface PMA energy density of 1.6 erg/cm2 were achieved by controlling the interfacial oxidation states through fine-tuning of oxidation processes and annealing temperature. Cross-sectional scanning transmission electron microscopy imaging revealed a lattice-matched Co2FeAl/MgAl2O4 interface, which may be responsible for the large PMA energy due to a reduction of the bulk anisotropy contribution.","" " Reliability of magnetic tunnel junctions with a spinel MgAl2O4 film ","Reliability of magnetic tunnel junctions with a spinel MgAl2O4 film","C.M. Choi, H. Sukegawa, S. Mitani, Y.H. Song","C.M. Choi, H. Sukegawa, S. Mitani, Y.H. Song"," Electronics Letters"," Electronics Letters","53","2","119","121","2017-01-19","TRUE","","scientific_journal","eng","","10.1049/el.2016.3007","","We investigated the stress-induced resistance drift and breakdown characteristics in MgAl2O4 (MAO)-based magnetic tunnel junctions (MTJs) with the MAO thickness of ∼0.9 nm. The occurrence of trap sites around the tunnel barrier–electrode interfaces was characterised via interval voltage stress (IVS) and constant voltage stress (CVS) experiments, in which the occurrence of trap sites affects the resistance drift in IVS and time-dependent dielectric breakdown in CVS. The observed resistance drift ratios were almost the same for positive and negative applied voltages, indicating that the difference in the interface structure was negligibly small between the top and bottom MAO/CoFe interfaces in the MAO-based MTJs. More interestingly, the resistance drift ratios were very low compa","" "Interdiffusion in epitaxial ultrathin Co2FeAl/MgO heterostructures with interface-induced perpendicular magnetic anisotropy","Interdiffusion in epitaxial ultrathin Co2FeAl/MgO heterostructures with interface-induced perpendicular magnetic anisotropy","Zhenchao Wen, Jason Paul Hadorn, Jun Okabayashi, Hiroaki Sukegawa, Tadakatsu Ohkubo, Koichiro Inomata, Seiji Mitani, Kazuhiro Hono","Zhenchao Wen, Jason Paul Hadorn, Jun Okabayashi, Hiroaki Sukegawa, Tadakatsu Ohkubo, Koichiro Inomata, Seiji Mitani, Kazuhiro Hono","Applied Physics Express","Applied Physics Express","10","1","013003","","2017-01-01","TRUE","","scientific_journal","eng","","10.7567/apex.10.013003","","The interfacial atomic structure of epitaxial ultrathin Co2FeAl/MgO(001) heterostructures, which is related to the interface-induced perpendicular magnetic anisotropy (PMA), was investigated using scanning transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray magnetic circular dichroism. Al atoms from the Co2FeAl layer significantly interdiffused into MgO, forming an Al-deficient CoFeAl/MgAlO structure near the Co2FeAl/MgO interface. This atomic replacement may have enhanced the PMA, which is consistent with the observed large perpendicular orbital magnetic moments of Fe atoms at the interface. This work suggests that control of interdiffusion at ferromagnet/barrier interfaces is critical for designing an interface-induced PMA system.","" "Li-substituted MgAl2O4barriers for spin-dependent coherent tunneling","Li-substituted MgAl2O4 barriers for spin-dependent coherent tunneling","Thomas Scheike, Hiroaki Sukegawa, Seiji Mitani","Thomas Scheike, Hiroaki Sukegawa, Seiji Mitani","Japanese Journal of Applied Physics","Japanese Journal of Applied Physics","55","11","110310","","2016-11-01","TRUE","","scientific_journal","eng","","10.7567/jjap.55.110310","","MgAl2O4にリチウムを一部置換させたLi-Mg-Al-Oエピタキシャル超薄膜をバリア層とする強磁性トンネル接合の作製に成功した。比較的高い120%の室温TMR比が得られるなど、MgAl2O4やMgOバリアで観察されるようなコヒーレントトンネル効果が実現され、4元系スピネル酸化物が良好なスピン依存伝導を示すことを明らかにした。","" "Tuning the magnetic properties and surface morphology of D022 Mn3-δGa films with high perpendicular magnetic anisotropy by N doping","Tuning the magnetic properties and surface morphology of D022 Mn3-δGa films with high perpendicular magnetic anisotropy by N doping","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Seiji Mitani, Kazuhiro Hono","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Seiji Mitani, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","109","15","152402","","2016-10-10","TRUE","","scientific_journal","eng","","10.1063/1.4964408","","We report the tunable magnetic properties and the smoothened surface morphology of epitaxial D022 Mn-Ga (Mn3Ga and Mn2.5Ga) films by N doping using reactive sputtering at 480C. The 50 nm thick Mn-Ga films grown with the N2/Ar gas flow rate (g) up to 0.66% showed 33%-50% reduction in the saturation magnetization compared to non-doped Mn-Ga. In particular, a single D022 phase was obtained in an optimal g range for Mn2.5Ga, resulted in the perpendicular magnetic anisotropy energy density of ~1MJ/m3 with 33% reduction in magnetization. Furthermore, the introduction of N provided the smoothened surface morphology at 50 nm thickness despite its high growth temperature, which is advantageous for thin film device applications.","" "Temperature dependence of reliability characteristics for magnetic tunnel junctions with a thin MgO dielectric film","Temperature dependence of reliability characteristics for magnetic tunnel junctions with a thin MgO dielectric film","Chul-Min Choi, Young-Taek Oh, Kyung-Jun Kim, Jin-Suk Park, Hiroaki Sukegawa, Seiji Mitani, Sung-Kyu Kim, Jeong-Yong Lee, Yun-Heub Song","Chul-Min Choi, Young-Taek Oh, Kyung-Jun Kim, Jin-Suk Park, Hiroaki Sukegawa, Seiji Mitani, Sung-Kyu Kim, Jeong-Yong Lee, Yun-Heub Song","Semiconductor Science and Technology","Semiconductor Science and Technology","31","7","075004","","2016-07-01","TRUE","","scientific_journal","eng","","10.1088/0268-1242/31/7/075004","","Temperature dependence of the reliability characteristics of magnetic tunnel junctions (MTJs) with a thin (1 nm thick) MgO dielectric film were investigated by numerical analyses based on the E-model, 1/E-model, and power-law voltage V-model, as well as by measuring time dependent dielectric breakdown (TDDB) degradation. Although the tunneling process giving rise to TDDB is still under debate, the temperature dependence of TDDB was much weaker using the 1/E model than the E-model or power-law model. The TDDB data measured experimentally in CoFeB/MgO/CoFeB MTJ devices also showed rather weak temperature dependence, in good agreement with the numerical results obtained from the 1/E-model considering the self-heating effect in MTJ devices.","" "Tunnel Magnetoresistance of Ferromagnetic Antiperovskite MnGaN/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions","Tunnel Magnetoresistance of Ferromagnetic Antiperovskite MnGaN/MgO/CoFeB Perpendicular Magnetic Tunnel Junctions","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Zhenchao Wen, Seiji Mitani, Kazuhiro Hono","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Zhenchao Wen, Seiji Mitani, Kazuhiro Hono","IEEE Transactions on Magnetics","IEEE Transactions on Magnetics","52","7","1","4","2016-07-01","TRUE","","scientific_journal","eng","","10.1109/tmag.2016.2519283","","We report on the tunnel magnetoresistance (TMR) effect of perpendicular magnetic tunnel junctions (p-MTJs) composed of a ferromagnetic antiperovskite MnGaN film with perpendicular magnetic anisotropy. The Mg insertion under the MgO barrier enhanced the perpendicular anisotropy of the top Fe/CoFeB layers with post-annealing process, and thus nearly perfect perpendicular magnetization was realized. A perpendicular TMR ratio up to 3.7%-3.8% was obtained at room temperature. The obtained low TMR ratio is mainly attributed to the imperfect MgO barrier, which includes many lattice-misfit dislocations at the MnGaN/MgO interface due to the large lattice mismatch of 8%. ","" "Effect of Mg insertion on time-dependent dielectric breakdown in MgO-based magnetic tunnel junctions","Effect of Mg insertion on time-dependent dielectric breakdown in MgO-based magnetic tunnel junctions","C.M. Choi, S. Mitani, H. Sukegawa, Y.H. Song","C.M. Choi, S. Mitani, H. Sukegawa, Y.H. Song","Electronics Letters","Electronics Letters","52","12","1037","1039","2016-06-09","TRUE","","scientific_journal","eng","","10.1049/el.2016.0686","","The stress-induced breakdown characteristics in magnesium oxide (MgO)-based magnetic tunnel junctions (MTJs) including an inserted Mg layer 0.5 nm thick is investigated, above or below an MgO tunnel barrier. Regardless of the insertion position, the inserted layer suppressed the time-dependent dielectric breakdown (TDDB) observed in the case of electron tunnelling into the Mg-inserted interface. This indicates that the Mg insertion significantly suppressed trap site formation at the anode-side barrier/electrode interface. The improvement of TDDB by the Mg insertion was confirmed through constant voltage stress experiments. ","" "Chemical ordering and large tunnel magnetoresistance in Co2FeAl/MgAl2O4/Co2FeAl(001) junctions","Chemical ordering and large tunnel magnetoresistance in Co2FeAl/MgAl2O4/Co2FeAl(001) junctions","Thomas Scheike, Hiroaki Sukegawa, Koichiro Inomata, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Thomas Scheike, Hiroaki Sukegawa, Koichiro Inomata, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Applied Physics Express","Applied Physics Express","9","5","053004","","2016-05-01","TRUE","","scientific_journal","eng","","10.7567/apex.9.053004","","スピネルバリアMTJではバリア層がスピネル構造に規則化する場合、「バンド折りたたみ」と呼ばれる効果によってTMR比の大きな低下が起こるという深刻な問題がある。本論文では、スピネル規則化バリアとともに高スピン偏極材料Co2FeAlをその上下層に用いることによって、このバンド折りたたみ問題を解決し、室温で340%を超える高いTMR比を実現した。","" "Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures","Spin-orbit torque in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO epitaxial magnetic heterostructures","Zhenchao Wen, Junyeon Kim, Hiroaki Sukegawa, Masamitsu Hayashi, Seiji Mitani","Zhenchao Wen, Junyeon Kim, Hiroaki Sukegawa, Masamitsu Hayashi, Seiji Mitani","AIP Advances","AIP Advances","6","5","056307","","2016-05-01","TRUE","","scientific_journal","eng","","10.1063/1.4944339","","We study the spin-orbit torque (SOT) effective fields in Cr/CoFeAl/MgO and Ru/CoFeAl/MgO magnetic heterostructures using the adiabatic harmonic Hall measurement. High-quality perpendicular-magnetic-anisotropy CoFeAl layers were grown on Cr and Ru layers. The magnitudes of the SOT effective fields were found to significantly depend on the underlayer material (Cr or Ru) as well as their thicknesses. The damping-like longitudinal effective field (ΔHL) increases with increasing underlayer thickness for all heterostructures. In contrast, the field-like transverse effective field (ΔHT) increases with increasing Ru thickness while it is almost constant or slightly decreases with increasing Cr thickness. ","" "Realization of high quality epitaxial current- perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001) wafer using NiAl buffer layer","NiAl下地層によるSi(001)基板上高品位エピタキシャルGMR素子の実現","Jiamin Chen, J. Liu, Y. Sakuraba, H. Sukegawa, S. Li, K. Hono","Jiamin Chen, J. Liu, Y. Sakuraba, H. Sukegawa, S. Li, K. Hono","APL Materials","APL Materials","4","5","056104","","2016-05-01","TRUE","","scientific_journal","eng","","10.1063/1.4950827","","In this letter, we report a NiAl buffer layer as a template for the integration of epitaxial current-perpendicular-plane-giant magnetoresistive (CPP-GMR) devices on a Si(001) single crystalline substrate. By depositing NiAl on a Si wafer 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 large magnetoresistive output comparable with that of the devices grown on an MgO(001) substrate, demonstrating the possibility of epitaxial spintronic devices with a NiAl templated Si wafer for practical applications.","" "Effect of Mg insertion on stress-induced resistance drift in MgO-based magnetic tunnel junctions","Effect of Mg insertion on stress-induced resistance drift in MgO-based magnetic tunnel junctions","C. M. Choi, Y.H. Song, J. Y. Lee, Y. T. Oh, H. Sukegawa, S. Mitani","C. M. Choi, Y.H. Song, J. Y. Lee, Y. T. Oh, H. Sukegawa, S. Mitani","Electronics Letters","Electronics Letters","52","7","531","533","2016-04-01","TRUE","","scientific_journal","eng","","10.1049/el.2015.4299","","The stress-induced resistance drift in MgO-based magnetic tunnel junctions (MTJs) with Mg insertion layer above and below a MgO tunnel barrier is investigated. Mg insertion suppresses the resistance drift. Resistance drift characteristics are improved when electrons tunnel into the Mg-inserted barrier/electrode interface, indicating that Mg insertion significantly suppresses trap site formation at the anode-side barrier/electrode interface. However, transmission electron microscopy images confirm that there is little difference in interface crystallinity between the Mg-inserted and non-inserted interfaces.","" "MgAl2O4(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target","MgAl2O4(001) based magnetic tunnel junctions made by direct sputtering of a sintered spinel target","Mohamed Belmoubarik, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Mohamed Belmoubarik, Hiroaki Sukegawa, Tadakatsu Ohkubo, Seiji Mitani, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","108","13","132404","","2016-03-28","TRUE","","scientific_journal","eng","","10.1063/1.4945049","","スピネルバリアMTJではFe電極を用いた場合でも室温200%を超えるTMR比を実現してきたが、主なバリア層作製にはMg-Al合金の後酸化処理を用いたものであり、低抵抗化に向けた平坦バリアが困難であった。本論文ではスピネル酸化物ターゲットからの直接スパッタによってより高品質スピネルバリアを作製でき、TMR比向上が可能であることが示され、実用的な作製手法を見出したことを報告する。","" "Influence of inverse spin Hall effect in spin-torque ferromagnetic resonance measurements","スピンホール強磁性共鳴法における逆スピンホール効果の影響","Kouta Kondou, Hiroaki Sukegawa, Shinya Kasai, Seiji Mitani, Yasuhiro Niimi, YoshiChika Otani","Kouta Kondou, Hiroaki Sukegawa, Shinya Kasai, Seiji Mitani, Yasuhiro Niimi, YoshiChika Otani","Applied Physics Express","Applied Physics Express","9","2","023002","","2016-02-01","TRUE","","scientific_journal","eng","","10.7567/apex.9.023002","","We have performed spectral analyses of spin-torque ferromagnetic resonance (ST-FMR) signals in both Ni 80Fe20/Ta and Co40Fe40B20/Ta bilayers and compared the spin Hall angles of these signals. We found tha t the contribution of the inverse spin Hall effect to the total signal in ST-FMR measurements is marke d particularly in the case of Co40Fe40B20/Ta bilayers, because the anisotropic magnetoresistance effec t in Co40Fe40B20, i.e., the origin of the ST-FMR signal, is much smaller than that in Ni80Fe20. When w e take into account the contribution of the inverse spin Hall effect, the spin Hall angle of Co40Fe40B 20/Ta decreases to less than half of that estimated by conventional ST-FMR spectral analysis.","" "Anisotropic magnetoresistance and current-perpendicular-to-plane giant magnetoresistance in epitaxial NiMnSb-based multilayers","エピタキシャルNiMnSb多層膜における異方性磁気抵抗効果と面直通電巨大磁気抵抗効果","B. Kwon, Y. Sakuraba, H. Sukegawa, S. Li, G. Qu, T. Furubayashi, K. Hono","B. Kwon, Y. Sakuraba, H. Sukegawa, S. Li, G. Qu, T. Furubayashi, K. Hono","Journal of Applied Physics","Journal of Applied Physics","119","2","023902","","2016-01-14","TRUE","","scientific_journal","eng","","10.1063/1.4939557","","We fabricated (001)-oriented C1b-NiMnSb epitaxial films on MgO substrate by a magnetron sputtering system and systematically investigated the structure, magnetic property, and anisotropic magnetoresistance (AMR) effect. NiMnSb film was deposited using a stoichiometric NiMnSb target which has Mn-deficient (Mn28.7 at. %) off-stoichiometric composition ratio. We have investigated bulk spin-polarization in NiMnSb films by measuring AMR on the basis of recent study for half-metallic L21-Heusler compounds. Although the negative sign of AMR ratio, which is indicative of half-metallic nature, was observed in the single layer NiMnSb films, the magnitude of AMR ratio (0.10% at RT) was about half of the largest value reported for half-metallic L21- Heusler compounds. The current-perpendicular-to-pl","" "Degradation Characteristics of MgO Based Magnetic Tunnel Junction Caused by Surface Roughness of Ta/Ru Buffer Layers","Degradation Characteristics of MgO Based Magnetic Tunnel Junction Caused by Surface Roughness of Ta/Ru Buffer Layers","Jung Min Lee, Chul Min Choi, Hiroaki Sukegawa, Jeong Yong Lee, Seiji Mitani, Yun-Heub Song","Jung Min Lee, Chul Min Choi, Hiroaki Sukegawa, Jeong Yong Lee, Seiji Mitani, Yun-Heub Song","Journal of Nanoscience and Nanotechnology","Journal of Nanoscience and Nanotechnology","16","1","654","657","2016-01-01","TRUE","","scientific_journal","eng","","10.1166/jnn.2016.11901","","We investigated how surface roughness of a Ta/Ru buffer layer affects the degradation characteristics on MgO-based magnetic tunnel junctions (MTJs). MTJs with worse surface roughness on the buffer layer showed increased resistance drift and degraded time-dependent dielectric breakdown (TDDB) characteristics. We suggest that this resulted from reduced MgO thickness on the MTJ with worse surface roughness on the buffer layer, which was estimated by the TDDB and analytic approach. As a result, surface roughness of the buffer layer is a critical factors that impacts the reliability of MTJs, and it should be controlled to have the smallest roughness value as possible.","" "Perpendicularly magnetized (001)-textured D022 MnGa films grown on an (Mg0.2Ti0.8)O buffer with thermally oxidized Si substrates","Perpendicularly magnetized (001)-textured D0(22) MnGa films grown on an (Mg0.2Ti0.8)O buffer with thermally oxidized Si substrates","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Seiji Mitani, Kazuhiro Hono","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Seiji Mitani, Kazuhiro Hono","Journal of Applied Physics","Journal of Applied Physics","118","16","163906","","2015-10-28","TRUE","","scientific_journal","eng","","10.1063/1.4934748","","We report the growth of (001)-textured polycrystalline D0(22) MnGa films with perpendicular magnetic anisotropy (PMA) on thermally oxidized Si substrates using an (Mg0.2Ti0.8)O (MTO) buffer layer. The ordered D0(22) MnGa film grown at the optimum substrate temperature of 530 degrees C on the MTO buffer layer shows PMA with magnetization of 80 kA/m, PMA energy density of 0.28 MJ/m(3), and coercivity of 2.3 T. The scanning transmission electron microscope analysis confirms the formation of a highly (001)-textured structure and the elementally sharp interfaces between the MTO layer and the MnGa layer. The achieved D022 MnGa PMA films on an amorphous substrate will provide the possible pathway of integration of a Mn-based PMA film into Si-based substrates.","" "Roadmap for Emerging Materials for Spintronic Device Applications","Roadmap for Emerging Materials for Spintronic Device Applications","Atsufumi Hirohata, Hiroaki Sukegawa, Hideto Yanagihara, Igor Zutic, Takeshi Seki, Shigemi Mizukami, Raja Swaminathan","Atsufumi Hirohata, Hiroaki Sukegawa, Hideto Yanagihara, Igor Zutic, Takeshi Seki, Shigemi Mizukami, Raja Swaminathan","IEEE Transactions on Magnetics","IEEE Transactions on Magnetics","51","10","1","11","2015-10-01","TRUE","","scientific_journal","eng","","10.1109/tmag.2015.2457393","","The Technical Committee of the IEEE Magnetics Society has selected seven research topics to develop their roadmaps, where major developments should be listed alongside expected timelines: 1) hard disk drives; 2) magnetic random access memories; 3) domain-wall devices; 4) permanent magnets; 5) sensors and actuators; 6) magnetic materials; and 7) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. ","" "Order parameters and magnetocrystalline anisotropy of off-stoichiometric D022 Mn2.36Ga epitaxial films grown on MgO (001) and SrTiO3 (001)","Order parameters and magnetocrystalline anisotropy of off-stoichiometric D022 Mn2.36Ga epitaxial films grown on MgO (001) and SrTiO3(001)","Hwachol Lee, Hiroaki Sukegawa, Seiji Mitani, Kazuhiro Hono","Hwachol Lee, Hiroaki Sukegawa, Seiji Mitani, Kazuhiro Hono","Journal of Applied Physics","Journal of Applied Physics","118","3","033904","","2015-07-21","TRUE","","scientific_journal","eng","","10.1063/1.4927039","","We study the relationship between long range order parameters and the magnetocrystalline anisotropy of off-stoichiometric D-022 Mn2.36Ga (MnGa) epitaxial films grown on MgO (001) and SrTiO3 (STO) (001) single crystalline substrates. MnGa films deposited on MgO (001) show rather large irregular variation in magnetization with increasing substrate temperature in spite of the improved long range order of total atomic sites. The specific site long range order of Mn-I site characterized in the [101] orientation revealed the fluctuation of the occupation fraction of two Mn atomic sites with elevated substrate temperature, which appears more relevant to the observed magnetization change than the long range order of the total atomic sites. In case of MnGa films grown on the lattice-matched STO (00","" "Ferromagnetic MnGaN thin films with perpendicular magnetic anisotropy for spintronics applications","Ferromagnetic MnGaN thin films with perpendicular magnetic anisotropy for spintronics applications","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Tadakatsu Ohkubo, Shinya Kasai, Seiji Mitani, Kazuhiro Hono","Hwachol Lee, Hiroaki Sukegawa, Jun Liu, Tadakatsu Ohkubo, Shinya Kasai, Seiji Mitani, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","107","3","032403","","2015-07-20","TRUE","","scientific_journal","eng","","10.1063/1.4927097","","Perpendicularly magnetized flat thin films of antiperovskite Mn67Ga24N9 were grown on an MgO(001) substrate by reactive sputtering using an argon/1% nitrogen gas mixture and a Mn70Ga30 target. The films showed a saturation magnetization of 80 ?100 kA/m, an effective perpendicular magnetic anisotropy (PMA) energy of 0.1?0.2 MJ/m3, and a Curie temperature of 660?740 K. Upon increasing the N composition, the films transformed from ferromagnetic to antiferromagnetic as expected in the stoichiometric Mn3GaN phase. Point contact Andreev reflection spectroscopy revealed that the ferromagnetic MnGaN has a current spin polarization of 57%, which is comparable to D022-MnGa. These findings suggest that MnGaN is a promising PMA layer for future spintronics devices.","" "Lattice-matched magnetic tunnel junctions using a Heusler alloy Co2FeAl and a cation-disorder spinel Mg-Al-O barrier","Lattice-matched magnetic tunnel junctions using a Heusler alloy Co2FeAl and a cation-disorder spinel Mg-Al-O barrier","Thomas Scheike, Hiroaki Sukegawa, Takao Furubayashi, Zhenchao Wen, Koichiro Inomata, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Thomas Scheike, Hiroaki Sukegawa, Takao Furubayashi, Zhenchao Wen, Koichiro Inomata, Tadakatsu Ohkubo, Kazuhiro Hono, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","105","24","242407","","2014-12-15","TRUE","","scientific_journal","eng","","10.1063/1.4904716","","Perfectly lattice-matched magnetic tunnel junctions (MTJs) consisting of a Heusler alloy B2-Co2FeAl (CFA) electrode and a cation-disorder spinel (Mg-Al-O) barrier were fabricated by sputtering and plasma oxidation. We achieved a large tunnel magnetoresistance (TMR) ratio of 228% at room temperature (RT) (398% at 5K) for the epitaxial CFA/MgAl-O/CoFe(001) MTJ, in which the effect of lattice defects on TMR ratios is excluded. With inserting a ultrathin (1.5 nm) CoFe layer between the CFA and Mg-Al-O, the TMR ratio further increased up to 280% at RT (453% at 5 K), which reflected the importance of controlling barrier-electrode interface states other than the lattice matching.","" "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, H. Sukegawa, Z.C. Wen, S. Yamamoto, S. Mitani, M. Tanaka, K. Inomata, S. Sugahara","R. Nakane, Y. Shuto, H. Sukegawa, Z.C. Wen, S. Yamamoto, S. Mitani, M. Tanaka, K. Inomata, S. Sugahara","Solid-State Electronics","Solid-State Electronics","102","","52","58","2014-12-01","TRUE","","scientific_journal","eng","","10.1016/j.sse.2014.06.004","","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 strongly depends on the surface roughness of the passivation film. Nevertheless, after the chip surface was atomically flattened by SiO2 deposition on it and successive chemical–mechanical polish (CMP) process for the surface, the fabricated MTJs on the chip 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","" "SPIN TRANSFER TORQUE SWITCHING AND PERPENDICULAR MAGNETIC ANISOTROPY IN FULL HEUSLER ALLOY Co2FeAl-BASED TUNNEL JUNCTIONS","Spin transfer torque switching and perpendicular magnetic anisotropy in full-Heusler alloy Co2FeAl-based tunnel junctions","H. SUKEGAWA, Z. C. WEN, S. KASAI, K. INOMATA, S. MITANI","H. SUKEGAWA, Z. C. WEN, S. KASAI, K. INOMATA, S. MITANI","SPIN","SPIN","04","04","1440023","","2014-12-01","TRUE","","scientific_journal","eng","","10.1142/s2010324714400232","","Some of Co-based full Heusler alloys have remarkable properties in spintronics, that is, high spin polarization of conduction electrons and low magnetic damping. Owing to these properties, magnetic tunnel junctions (MTJs) using Co-based full Heusler alloys are potentially of particular importance for spintronic application such as magnetoresistive random access memories (MRAMs). Recently, we have ¯rst demonstrated spin transfer torque (STT) switching and perpendicular magnetic anisotropy (PMA), which are required for developing high-density MRAMs, in full-Heusler Co2FeAl alloy-based MTJs. In this review, the main results of the experimental demonstrations are shown with referring to related issues, and the prospect of MTJs using Heusler alloys is also discussed.","" "A 4-Fold-Symmetry Hexagonal Ruthenium for Magnetic Heterostructures Exhibiting Enhanced Perpendicular Magnetic Anisotropy and Tunnel Magnetoresistance","A 4-fold symmetry hexagonal ruthenium for magnetic heterostructures exhibiting enhanced perpendicular magnetic anisotropy tunnel","Zhenchao Wen, Hiroaki Sukegawa, Takao Furubayashi, Jungwoo Koo, Koichiro Inomata, Seiji Mitani, Jason Paul Hadorn, Tadakatsu Ohkubo, Kazuhiro Hono","Zhenchao Wen, Hiroaki Sukegawa, Takao Furubayashi, Jungwoo Koo, Koichiro Inomata, Seiji Mitani, Jason Paul Hadorn, Tadakatsu Ohkubo, Kazuhiro Hono","Advanced Materials","Advanced Materials","26","37","6483","6490","2014-10-01","TRUE","","scientific_journal","eng","","10.1002/adma.201401959","","MRAM等の開発において注目されているホイスラー合金薄膜の界面垂直磁気異方性について研究を行った。Ruバッファー層を用いることで、垂直磁気異方性が大幅に増大することを発見するとともに、磁気抵抗比についてもよい値が得られた。構造解析により、このRuバッファー層は(023)面がMgO(001)基板やホイスラー合金の(001)面とエピタキシャル成長するという新規な構造を有することが分かった。磁気記録媒体等への応用の可能性も検討できる重要な基礎技術である。","" "Interface perpendicular magnetic anisotropy in Fe/MgAl2O4layered structures","Interface perpendicular magnetic anisotropy in Fe/MgAl2O4 layered structures","Jungwoo Koo, Hiroaki Sukegawa, Seiji Mitani","Jungwoo Koo, Hiroaki Sukegawa, Seiji Mitani","physica status solidi (RRL) - Rapid Research Letters","physica status solidi (RRL) - Rapid Research Letters","8","10","841","844","2014-10-01","TRUE","","scientific_journal","eng","","10.1002/pssr.201409340","","The recently reported MgAl2O4 tunnel barrier for the magnetictunnel junctions (MTJs) is considered to be an alternative to the conventional MgO barrier, since a large tunnel magnetoresistance (TMR) ratio was obtained for the MgAl2O4-based MTJs. In this study, we demonstrated large perpendicular magnetic anisotropy (PMA) arising from the interfaces of Fe(001)/MgAl2O4 layered structures, which can be useful for developing perpendicularly magnetized MgAl2O4-based MTJs. A PMA energy density of 0.4 MJ/m3 was achieved for an epitaxially grown 0.7 nm thick Fe/MgAl2O4(001). Interestingly, the interface PMA was also obtained for the Fe/nonepitaxially grown MgAl2O4 structures, which indicates that the crystallographic structure of MgAl2O4 layer has no critical influence on the obtained PMA.","" "Perpendicular magnetic anisotropy at the interface between ultrathin Fe film and MgO studied by angular-dependent x-ray magnetic circular dichroism","Perpendicular magnetic anisotropy at the interface between ultrathin Fe film and MgO studied by angular-dependent x-ray magnetic circular dichroism","J. Okabayashi, J. W. Koo, H. Sukegawa, S. Mitani, Y. Takagi, T. Yokoyama","J. Okabayashi, J. W. Koo, H. Sukegawa, S. Mitani, Y. Takagi, T. Yokoyama","Applied Physics Letters","Applied Physics Letters","105","12","122408","","2014-09-22","TRUE","","scientific_journal","eng","","10.1063/1.4896290","","Interface perpendicular magnetic anisotropy (PMA) in ultrathin Fe/MgO (001) has been investigated using angular-dependent magnetic circular dichroism (XMCD). We found that anisotropic orbital magnetic moments deduced from the analysis of XMCD contribute to the large PMA energies, whose values depend on the annealing temperature. The large PMA energies determined from magnetization measurements (Koo et al., Appl. Phys. Lett. 103, 192401 (2013).) are related to those estimated from the XMCD and the anisotropic orbital magnetic moments through the spin-orbit interaction. The enhancement of anisotropic orbital magnetic moments can be explained mainly by the hybridization between the Fe 3dz2 and O 2pz states.","" "Post-oxidized Mg-Al-O(001) coherent tunneling barrier in a wide range of resistance-area products","Post-oxidized Mg-Al-O(001) coherent tunneling barrier in a wide range of resistance-area products","Hiroaki Sukegawa, Koichiro Inomata, Seiji Mitani","Hiroaki Sukegawa, Koichiro Inomata, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","105","9","092403","","2014-09-01","TRUE","","scientific_journal","eng","","10.1063/1.4895104","","We fabricated epitaxial Mg-Al-O(001) tunnel barriers using direct/indirect plasma oxidation and natural oxidation of an MgAl layer for use in Fe/Mg-Al-O/Fe magnetic tunnel junctions. All the oxidation processes formed epitaxial Mg-Al-O barriers, and a wide resistance area (RA) product range and large tunnel magnetoresistance (TMR) ratios at room temperature were achieved by optimizing the MgAl thickness (tMgAl). Near optimum oxidation conditions and tMgAl, small bias voltage dependence of the TMR ratio, and distinct local minima in the dI/dV spectra for the parallel magnetic configuration were observed, indicating that coherent tunneling transport was significant. This study showed that Mg-Al-O coherent tunnel barriers have excellent formability in a wide RA product range.","" "Magnetotransport properties in perpendicularly magnetized tunnel junctions using an ultrathin Fe electrode","Magnetotransport properties in perpendicularly magnetized tunnel junctions using an ultrathin Fe electrode","J W Koo, H Sukegawa, S Kasai, Z C Wen, S Mitani","J W Koo, H Sukegawa, S Kasai, Z C Wen, S Mitani","Journal of Physics D: Applied Physics","Journal of Physics D: Applied Physics","47","32","322001","","2014-08-13","TRUE","","scientific_journal","eng","","10.1088/0022-3727/47/32/322001","","The tunnel magnetoresistance (TMR) effect was investigated in perpendicularly magnetized magnetic tunnel junctions (p-MTJs) consisting of the stacked layer structure of ultrathin Fe (0.7)/MgO (1.8)/CoFeB (1.2–1.4) (in nm). A relatively large TMR ratio of 95 % was obtained with an interface perpendicular magnetic anisotropy energy density of 1.5 mJ/m2 at the Fe/MgO interface. Moreover, we found that the p-MTJ exhibits spin-dependent resonant tunneling characteristics in the bias voltage dependence of differential conductance, corresponding to a quantum well confined in five monolayers of Fe(001) atomic plane. ","" "Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in PolycrystallineCo2FeAlFull-Heusler-Alloy Magnetic Tunnel Junctions on AmorphousSi/SiO2Substrates","Tunnel Magnetoresistance and Spin-Transfer-Torque Switching in PolycrystallineCo2FeAlFull-Heusler-Alloy Magnetic Tunnel Junctions on AmorphousSi/SiO2Substrates","Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Koichiro Inomata, Seiji Mitani","Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Koichiro Inomata, Seiji Mitani","Physical Review Applied","Physical Review Applied","2","2","","","2014-08-01","TRUE","","scientific_journal","eng","","10.1103/physrevapplied.2.024009","","We study polycrystalline Co2FeAl (CFA) full-Heusler-alloy-based magnetic tunnel junctions (MTJs) fabricated on a Si/SiO2 amorphous substrate. A tunnel magnetoresistance ratio up to 175% is obtained for a MTJ with a CFA/MgO/CoFe structure on a 7.5-nm-thick MgO buffer. Spin-transfer-torque-induced magnetization switching is also achieved in the MTJs with a 2-nm-thick polycrystalline CFA film as a switching layer. The intrinsic critical current density (Jc0) is determined to be 8.2 x 10^6 A/cm2, which is lower than that for epitaxial CFA MTJs. We find that the Gilbert damping constant is approximately 0.015 and is almost independent of the CFA thickness. The low Jc0 for the polycrystalline MTJ is mainly attributed to the low α of the CFA layer.","" "Direct Synthesis of MOF-Derived Nanoporous Carbon with Magnetic Co Nanoparticles toward Efficient Water Treatment","効率的な水処理に向けた磁性Coナノ粒子とMOF由来ナノポーラスカーボンの直接合成","Nagy L. Torad, Ming Hu, Shinsuke Ishihara, Hiroaki Sukegawa, Alexis A. Belik, Masataka Imura, Katsuhiko Ariga, Yoshio Sakka, Yusuke Yamauchi","Nagy L. Torad, Ming Hu, Shinsuke Ishihara, Hiroaki Sukegawa, Alexis A. Belik, Masataka Imura, Katsuhiko Ariga, Yoshio Sakka, Yusuke Yamauchi","Small","Small","10","10","2096","2107","2014-05-01","TRUE","","scientific_journal","eng","","10.1002/smll.201302910","","Nanoporous carbon particles with magnetic Co nanoparticles (Co/NPC particles) are synthesized by one-step carbonization of zeolitic imidazolate framework-67 (ZIF-67) crystals. After the carbonization, the original ZIF-67 shapes are preserved well. Fine magnetic Co nanoparticles are well dispersed in the nanoporous carbon matrix, with the result that the Co/NPC particles show a strong magnetic response. The obtained nanoporous carbons show a high surface area and well-developed graphitized wall, thereby realizing fast molecular diffusion of methylene blue (MB) molecules with excellent adsorption performance. The Co/NPC possesses an impressive saturation capacity for MB dye compared with the commercial activated carbon. ","" "Quantitative analysis of anisotropic magnetoresistance in Co2MnZ and Co2FeZ epitaxial thin films: A facile way to investigate spin-polarization in half-metallic Heusler compounds","Co2MnZとCo2FeZエピタキシャル薄膜における異方性磁気抵抗効果の定量解析 : ハーフメタルホイスラー合金におけるスピン偏極率の効率的測","Y. Sakuraba, S. Kokado, Y. Hirayama, T. Furubayashi, H. Sukegawa, S. Li, Y. K. Takahashi, K. Hono","Y. Sakuraba, S. Kokado, Y. Hirayama, T. Furubayashi, H. Sukegawa, S. Li, Y. K. Takahashi, K. Hono","Applied Physics Letters","Applied Physics Letters","104","17","172407","","2014-04-28","TRUE","","scientific_journal","eng","","10.1063/1.4874851","","nisotropic magnetoresistance (AMR) effect has been systematically investigated in various Heusler compounds Co2MnZ and Co2FeZ epitaxial films and quantitatively summarized against the total valence electron number NV. The sign of AMR ratio changes from negative to positive when NV becomes below 28.2 and above 30.3, indicating that the Fermi level overlaps with the valence and conduction band edges of half-metallic gap, respectively. We also find out that the magnitude of negative AMR ratio gradually increases with shifting of EF away from the gap edges, and there is a clear positive correlation between the magnitude of negative AMR ratio and magnetoresistive output of the giant magnetoresistive devices using the Heusler compounds. This indicates that AMR can be used as a facile way to opti","" "Effect of an interface Mg insertion layer on the reliability of a magnetic tunnel junction based on a Co2FeAl full-Heusler alloy","Effect of an interface Mg insertion layer on the reliability of a magnetic tunnel junction based on a Co2FeAl full-Heusler alloy","Jung-Min Lee, Gyu Hyun Kil, Gae Hun Lee, Chul Min Choi, Yun-Heub Song, Hiroaki Sukegawa, Seiji Mitani","Jung-Min Lee, Gyu Hyun Kil, Gae Hun Lee, Chul Min Choi, Yun-Heub Song, Hiroaki Sukegawa, Seiji Mitani","Journal of the Korean Physical Society","Journal of the Korean Physical Society","64","8","1144","1149","2014-04-01","TRUE","","scientific_journal","eng","","10.3938/jkps.64.1144","","The reliability of a magnetic tunnel junction (MTJ) based on a Co2FeAl (CFA) full-Heusler alloy with a MgO tunnel barrier was evaluated. In particular, the effect of a Mg insertion layer under the MgO was investigated in view of resistance drift by using various voltage stress tests. We compared the resistance change during constant voltage stress (CVS) and confirmed a trap/detrap phenomenon during the interval stress test for samples with and without a Mg insertion layer. The MTJ with a Mg insertion layer showed a relatively small resistance change for the CVS test and a reduced trap/detrap phenomenon for the interval stress test compared to the sample without a Mg insertion layer. ","" "Modulation of effective damping constant using spin Hall effect","スピンホール効果を用いた有効ダンピングの変調","Shinya Kasai, Kouta Kondou, Hiroaki Sukegawa, Seiji Mitani, Kazuhito Tsukagoshi, Yoshichika Otani","Shinya Kasai, Kouta Kondou, Hiroaki Sukegawa, Seiji Mitani, Kazuhito Tsukagoshi, Yoshichika Otani","Applied Physics Letters","Applied Physics Letters","104","9","092408","","2014-03-03","TRUE","","scientific_journal","eng","","10.1063/1.4867649","","We have investigated modulation of the effective damping constant aeff via spin currents through the spin Hall effect for Permalloy/Pt bilayer films with various thicknesses. The observed linear and sinusoidal dependences of current density and field direction on aeff are in agreement with the analytical model. By comparing the thickness dependence of spin Hall angle obtained from the damping modulation with that previously obtained by spin-torque-induced ferromagnetic resonance, we show that there is no clear extrinsic contribution in the present method. We also show the large modulation of the effective damping constant (down to 20%) in the high-current-density region. ","" "Thickness dependence of spin torque ferromagnetic resonance in Co75Fe25/Pt bilayer films","CoFe/Pt二層膜におけるスピン流誘起強磁性共鳴:膜厚依存性","A. Ganguly, K. Kondou, H. Sukegawa, S. Mitani, S. Kasai, Y. Niimi, Y. Otani, A. Barman","A. Ganguly, K. Kondou, H. Sukegawa, S. Mitani, S. Kasai, Y. Niimi, Y. Otani, A. Barman","Applied Physics Letters","Applied Physics Letters","104","7","072405","","2014-02-17","TRUE","","scientific_journal","eng","","10.1063/1.4865425","","The spin Hall angle of Pt in Co75Fe25/Pt bilayer films was experimentally investigated by means of the spin-torque ferromagnetic resonance and the modulation of damping measurements. By comparing the present results with the Ni80Fe20/Pt system, we found that the ferromagnetic layer underneath the Pt one greatly affects the estimation of the spin Hall angle. We also discuss the spin diffusion length of Pt and the ferromagnetic thickness dependence of the Gilbert damping coefficient.","" "Synthesis of porous iron oxide microspheres by a double hydrophilic block copolymer","二重親水性ブロックコポリマーによる多孔質酸化鉄マイクロスフィアの合成","B. P. Bastakoti, Hiroaki Sukegawa, Kevin C.-W. Wu, Yusuke Yamauchi","B. P. Bastakoti, Hiroaki Sukegawa, Kevin C.-W. Wu, Yusuke Yamauchi","RSC Advances","RSC Advances","4","20","9986","","2014-01-14","TRUE","","scientific_journal","eng","","10.1039/c3ra47490a","","Porous microspheres of iron oxide (Fe2O3) are synthesized using a double hydrophilic block copolymer of poly(ethylene oxide)-block-poly(acrylic acid) (PEO-b-PAA). The PAA block with negative charge strongly interacts with ferric ions. The assembly of primary nanoparticles at elevated temperature forms the porous microsphere of Fe2O3. The MTT assay of the microspheres based on HepG2 cell indicates good biocompatibility. The thorough porosity of microspheres can accommodate a large amount of anticancer drug cisplatin.","" "Large perpendicular magnetic anisotropy at Fe/MgO interface","Large perpendicular magnetic anisotropy at Fe/MgO interface","J. W. Koo, S. Mitani, T. T. Sasaki, H. Sukegawa, Z. C. Wen, T. Ohkubo, T. Niizeki, K. Inomata, K. Hono","J. W. Koo, S. Mitani, T. T. Sasaki, H. Sukegawa, Z. C. Wen, T. Ohkubo, T. Niizeki, K. Inomata, K. Hono","Applied Physics Letters","Applied Physics Letters","103","19","192401","","2013-11-04","TRUE","","scientific_journal","eng","","10.1063/1.4828658","","A large perpendicular magnetic anisotropy (PMA) of 1.4 MJ/m3 was observed from ultrathin Fe/MgO(001) bilayers grown on Cr-buffered MgO(001). The PMA strongly depends on the surface state of Fe prior to the MgO deposition. A large PMA energy density of 1.4 MJ/m3 was achieved for a 0.7 nm thick Fe layer having adsorbate-induced surface reconstruction, which is likely to originate from oxygen atoms floating up from the Cr buffer layer. This large magnitude of PMA satisfies the criterion that is required for thermal stability of magnetization in a few tens nanometer-sized magnetic memory elements.","" "Low-resistive monocrystalline Mg-Al-O barrier magnetic tunnel junctions for spin-transfer magnetization switching","Low-resistive monocrystalline Mg-Al-O barrier magnetic tunnel junctions for spin-transfer magnetization switching","Hiroaki Sukegawa, Seiji Mitani, Tadakatsu Ohkubo, Koichiro Inomata, Kazuhiro Hono","Hiroaki Sukegawa, Seiji Mitani, Tadakatsu Ohkubo, Koichiro Inomata, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","103","14","142409","","2013-09-30","TRUE","","scientific_journal","eng","","10.1063/1.4824134","","Monocrystalline Mg-Al-O barriers for magnetic tunnel junctions (MTJs) were fabricated by natural oxidation of Mg-Al thin films. The naturally oxidized Mg-Al-O barrier had a cation-disorder MgAl2O4 structure, and Fe/Mg-Al-O/Fe(001) MTJs showed a tunnel magnetoresistance (TMR) ratio of over 180% at room temperature. In addition, the natural oxidation process resulted in tunnel barriers with a resistance area product (RA) of less than 5 Xlm2. We observed clear magnetization switching in a CoFe/Mg-Al-O/CoFe MTJ by spin-transfer torque. These results indicate that the natural oxidation of Mg-Al alloy is an effective method for processing cationdisorder MgAl2O4 barrier for coherent TMR with low RA.","" "Temperature dependence of magnetoresistive output of pseudo spin valves with Co2Fe(Al1−xSix) Heusler alloys and a Ag spacer","Co2Fe(Al1-xSix) ホイスラー合金とAgスペーサーを用いた擬スピンバルブの磁気抵抗出力の温度依存性","T. Furubayashi, T. M. Nakatani, H. S. Goripati, H. Sukegawa, Y. K. Takahashi, K. Inomata, K. Hono","T. Furubayashi, T. M. Nakatani, H. S. Goripati, H. Sukegawa, Y. K. Takahashi, K. Inomata, K. Hono","Journal of Applied Physics","Journal of Applied Physics","114","12","123910","","2013-09-28","TRUE","","scientific_journal","eng","","10.1063/1.4821243","","We investigated the temperature dependence of magnetoresistive (MR) outputs of current-perpendicular-to-plane pseudo spin valves (CPP PSV) with Co2FeAl1-xSix (0<x<1) Heusler alloy ferromagnetic layers and a Ag spacer layer to optimize x. The MR ratios at room temperature do not show x dependence, while the MR ratios measured at 5 K showed strong x dependence; the largest resistance change-area product ΔRA = 21 mΩ•μm2 was obtained for x=1 and ΔRA decreased with decreasing x. The results apparently contradicts with the theoretical prediction that the highest spin polarization is attained for x=0.5. The discrepancy is due to the structural origin that the L21 order is obtained only in the Co2FeSi alloy film.","" "Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dichroism","Large anisotropic Fe orbital moments in perpendicularly magnetized Co2FeAl Heusler alloy thin films revealed by angular-dependent x-ray magnetic circular dicroism","Jun Okabayashi, Hiroaki Sukegawa, Zhenchao Wen, Koichiro Inomata, Seiji Mitani","Jun Okabayashi, Hiroaki Sukegawa, Zhenchao Wen, Koichiro Inomata, Seiji Mitani","Applied Physics Letters","Applied Physics Letters","103","10","102402","","2013-09-02","TRUE","","scientific_journal","eng","","10.1063/1.4819915","","Perpendicular magnetic anisotropy (PMA) in Heusler alloy Co2FeAl thin films sharing an interface with a MgO layer is investigated by angular-dependent x-ray magnetic circular dichroism. Orbital and spin magnetic moments are deduced separately for Fe and Co 3d electrons. In addition, the PMA energies are estimated using the orbital magnetic moments parallel and perpendicular to the film surfaces. We found that PMA in Co2FeAl is determined mainly by the contribution of Fe atoms with large orbital magnetic moments, which are enhanced at the interface between Co2FeAl and MgO. Furthermore, element specific magnetization curves of Fe and Co are found to be similar, suggesting the existence of ferromagnetic coupling between Fe and Co PMA directions.","" "Enhanced tunnel magnetoresistance in a spinel oxide barrier with cation-site disorder","Enhanced tunnel magnetoresistance in a spinel oxide barrier with cation-site disorder","Hiroaki Sukegawa, Yoshio Miura, Shingo Muramoto, Seiji Mitani, Tomohiko Niizeki, Tadakatsu Ohkubo, Kazutaka Abe, Masafumi Shirai, Koichiro Inomata, Kazuhiro Hono","Hiroaki Sukegawa, Yoshio Miura, Shingo Muramoto, Seiji Mitani, Tomohiko Niizeki, Tadakatsu Ohkubo, Kazutaka Abe, Masafumi Shirai, Koichiro Inomata, Kazuhiro Hono","Physical Review B","Physical Review B","86","18","","","2012-11-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.86.184401","","We report enhanced tunnel magnetoresistance (TMR) ratios of 188% (308%) at room temperature and 328% (479%) at 15 K for cation-site-disorderedMgAl2O4-barrier magnetic tunnel junctions (MTJs) with Fe (Fe0.5Co0.5 alloy) electrodes, which exceed the TMR ratios theoretically calculated and experimentally observed for ordered spinel barriers. The enhancement of TMRratios is attributed to the suppression of the so-called band-folding effect in ordered spinel MTJs [Phys. Rev. B 86, 024426 (2012)]. First-principles calculations describe a dominant role of the oxygen sublattice for spin-dependent coherent tunneling, suggesting a mechanism of coherent tunneling occurring even in the disordered systems.","" "The effect of interfaces on magnetic activation volumes in single crystal Co2FeSi Heusler alloy thin films","The effect of interfaces on magnetic activation volumes in single crystal Co2FeSi Heusler alloy thin films","J. Sagar, H. Sukegawa, L. Lari, V. K. Lazarov, S. Mitani, K. O'Grady, A. Hirohata","J. Sagar, H. Sukegawa, L. Lari, V. K. Lazarov, S. Mitani, K. O'Grady, A. Hirohata","Applied Physics Letters","Applied Physics Letters","101","10","102410","","2012-09-03","TRUE","","scientific_journal","eng","","10.1063/1.4749822","","Structural and magnetization reversal studies have been carried out on single crystal Co2FeSi thin films grown on MgO (001) substrates. The films are highly L21 ordered after annealing above 500 degC. Magnetization reversal has been investigated by measurements of the activation volumes (Vact) within the films. This volume represents the unit of reversal in a magnetic material. Vact (4x10^3 nm^3) has been found to be independent of the physical structure. Vact is found to correspond to an array of periodic misfit dislocations at the Co2FeSi/MgO interface. Such a small Vact potentially prevents coherent magnetization reversal as required for giant magnetoresistance or tunnel magnetoresistance devices.","" "Evaluation of Spin Hall Angle and Spin Diffusion Length by Using Spin Current-Induced Ferromagnetic Resonance","スピン流誘起強磁性共鳴を用いたスピンホール角とスピン拡散長の評価","Kouta Kondou, Hiroaki Sukegawa, Seiji Mitani, Kazuhito Tsukagoshi, Shinya Kasai","Kouta Kondou, Hiroaki Sukegawa, Seiji Mitani, Kazuhito Tsukagoshi, Shinya Kasai","Applied Physics Express","Applied Physics Express","5","7","073002","","2012-07-01","TRUE","","scientific_journal","eng","","10.1143/apex.5.073002","","スピントロニクスにおいて、電流ースピン流の相互変換はもっとも重要な研究課題の一つである。近年、スピン流を生成する新規手法として、スピンホール効果が提案および実証された。しかし、電流ースピン流変換効率、いわゆるスピンホール角はスピンホール効果におけるもっとも重要な物理量であるのにもかかわらず、定量的な評価がなされていなかった。本論文では強磁性ー非磁性二層膜において、スピン流誘起強磁性共鳴によるスピンホール角とスピン拡散長の評価について報告したものである。強磁性体および非磁性体の膜厚依存性を詳細に調べることによって、スピンホール角とスピン拡散長の評価に膜厚が影響を与えること、またこれらの寄与を取り除くことによって、スピンホール角の正確な評価が可能となることを示した。","" "Magnetic Tunnel Junctions with Perpendicular Anisotropy Using a Co$_{2}$FeAl Full-Heusler Alloy","Magnetic Tunnel Junctions with Perpendicular Anisotropy Using a Co$_{2}$FeAl Full-Heusler Alloy","Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Masamitsu Hayashi, Seiji Mitani, Koichiro Inomata","Zhenchao Wen, Hiroaki Sukegawa, Shinya Kasai, Masamitsu Hayashi, Seiji Mitani, Koichiro Inomata","Applied Physics Express","Applied Physics Express","5","6","063003","","2012-06-01","TRUE","","scientific_journal","eng","","10.1143/apex.5.063003","","We fabricated perpendicularly magnetized magnetic tunnel junctions (p-MTJs) with an ultrathin Co2FeAl (CFA) full-Heusler alloy electrode having large interface magnetic anisotropy of CFA/MgO. An out-of-plane tunnel magnetoresistance (TMR) ratio of 53% at room temperature was observed in CFA/MgO/Co20Fe60B20 p-MTJs. By inserting a 0.1-nm-thick Fe (Co50Fe50) layer between the MgO and Co20Fe60B20 layers, The TMR ratio was significantly enhanced to 91% (82%) due to the improved interface. The bias voltage dependence of differential conductance did not clearly show coherent tunneling characteristics for ultrathin CFA-MTJs, suggesting that a higher TMR ratio may be achieved by improving the B2 ordering of CFA and/or interface structure.","" "Signature of Coherent Transport in Epitaxial Spinel-Based Magnetic Tunnel Junctions Probed by Shot Noise Measurement","Signature of Coherent Transport in Epitaxial Spinel-Based Magnetic Tunnel Junctions Probed by Shot Noise Measurement","Takahiro Tanaka, Tomonori Arakawa, Kensaku Chida, Yoshitaka Nishihara, Daichi Chiba, Kensuke Kobayashi, Teruo Ono, Hiroaki Sukegawa, Shinya Kasai, Seiji Mitani","Takahiro Tanaka, Tomonori Arakawa, Kensaku Chida, Yoshitaka Nishihara, Daichi Chiba, Kensuke Kobayashi, Teruo Ono, Hiroaki Sukegawa, Shinya Kasai, Seiji Mitani","Applied Physics Express","Applied Physics Express","5","5","053003","","2012-05-01","TRUE","","scientific_journal","eng","","10.1143/apex.5.053003","","We measured the shot noise in fully epitaxial Fe/MgAl2OX /Fe-based magnetic tunneling junctions (MTJs). While the Fano factor to characterize the shot noise is very close to unity in the antiparallel configuration, it is reduced to 0.98 in the parallel configuration. This observation shows the sub-Poissonian process of electron tunneling in the parallel configuration, indicating the coherent tunneling through the spinel-based tunneling barrier of the MTJs.","" "Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions","Spin-transfer switching in full-Heusler Co2FeAl-based magnetic tunnel junctions","Hiroaki Sukegawa, Zhenchao Wen, Kouta Kondou, Shinya Kasai, Seiji Mitani, Koichiro Inomata","Hiroaki Sukegawa, Zhenchao Wen, Kouta Kondou, Shinya Kasai, Seiji Mitani, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","100","18","182403","","2012-04-30","TRUE","","scientific_journal","eng","","10.1063/1.4710521","","We demonstrated spin-transfer magnetization switching using magnetic tunnel junctions (MTJs) with a full-Heusler alloy Co2FeAl (CFA). We prepared CFA (1.5 nm)/MgO/CoFe (4 nm) (“CFA-free”) and CFA (30 nm)/MgO/CoFeB (2 nm) (“CFA-reference”) MTJs on a Cr(001) layer. The intrinsic critical current density (Jc0) of the CFA-free (CFA-reference) MTJ was 29 MA/cm2 (7.1 MA/cm2). The larger Jc0 of the CFA-free MTJ is attributed to the significant enhancement of the Gilbert damping factor (0.04) of the CFA due to the Cr layer. The Jc0 of the CFA-reference is as small as that reported for typical CoFeB/MgO/CoFeB MTJs.","" "59Co NMR experiment as a probe of electron doping in Co2FeAl1−xSixHeusler alloys","59Co NMR experiment as a probe of electron doping in Co2FeAl1−xSixHeusler alloys","M. Wójcik, E. Jedryka, H. Sukegawa, T. Nakatani, K. Inomata","M. Wójcik, E. Jedryka, H. Sukegawa, T. Nakatani, K. Inomata","Physical Review B","Physical Review B","85","10","","","2012-03-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.85.100401","","A systematic 59Co NMR study has been carried out at 4.2 K in a series of quaternary Co2FeAl1-xSix polycrystalline bulk Heusler alloys (x = 0, 0.3, 0.5, 0.7, 1). It was shown that the effect of Si substitution consists in a significant modification of 59Co hyperfine field and that this modification is mainly due to the contribution from s valence electron polarization, suggesting a shift of the Fermi energy level inside the half-metallic gap. This observation supports the theoretical predictions that the Fermi-level position in Co2FeZ Heusler alloys can be effectively tuned by varying the composition of the Z sublattice.","" "Synthesis of Prussian Blue Nanoparticles with a Hollow Interior by Controlled Chemical Etching","化学エッチングによる内部が空洞のプルーシャンブルーナノ粒子の合成","Ming Hu, Shuhei Furukawa, Ryo Ohtani, Hiroaki Sukegawa, Yoshihiro Nemoto, Julien Reboul, Susumu Kitagawa, Yusuke Yamauchi","Ming Hu, Shuhei Furukawa, Ryo Ohtani, Hiroaki Sukegawa, Yoshihiro Nemoto, Julien Reboul, Susumu Kitagawa, Yusuke Yamauchi","Angewandte Chemie International Edition","Angewandte Chemie International Edition","51","4","984","988","2012-01-23","TRUE","","scientific_journal","eng","","10.1002/anie.201105190","","Hollow particles, an important class of materials with large internal cavities and thin shells, present a wide range ofpotential applications, such as energy storage, chemical catalysis, photonics, and biomedical carriers. The properties of hollow particles are strongly affected by the compositions and exquisite nanostructures of the shell regions. Many efforts have been made to control these parameters. Recently, hollow particles with nanoporous shells have attracted great interest because the large pore volumes and high surface areas provided by the nanoporous shells show large storage capacity and allow guest species to pass easily into the internal cavity. For instance, metal oxide hollow particles present a superior lithium storage capacity and good cycle performance, which could impr","" "Spin Polarimetry and Magnetic Dichroism on a Buried Magnetic Layer Using Hard X-ray Photoelectron Spectroscopy","Spin Polarimetry and Magnetic Dichroism on a Buried Magnetic Layer Using Hard X-ray Photoelectron Spectroscopy","Gregory Stryganyuk, Xeniya Kozina, Gerhard H. Fecher, Siham Ouardi, Stanislav Chadov, Claudia Felser, Gerd Schönhense, Pavel Lushchyk, Andreas Oelsner, Pasqual Bernhard, Eiji Ikenaga, Takeharu Sugiyama, Hiroaki Sukegawa, Zhenchao Wen, Koichiro Inomata, Keisuke Kobayashi","Gregory Stryganyuk, Xeniya Kozina, Gerhard H. Fecher, Siham Ouardi, Stanislav Chadov, Claudia Felser, Gerd Schönhense, Pavel Lushchyk, Andreas Oelsner, Pasqual Bernhard, Eiji Ikenaga, Takeharu Sugiyama, Hiroaki Sukegawa, Zhenchao Wen, Koichiro Inomata, Keisuke Kobayashi","Japanese Journal of Applied Physics","Japanese Journal of Applied Physics","51","1","016602","","2012-01-01","TRUE","","scientific_journal","eng","","10.1143/jjap.51.016602","","The spin-resolved electronic structure of buried magnetic layers is studied by hard X-ray photoelectron spectroscopy (HAXPES) using a spin polarimeter in combination with a high-energy hemispherical electron analyzer at the high-brilliance BL47XU beamline (SPring-8, Japan). Spinresolved photoelectron spectra are analyzed in comparison with the results of magnetic linear and circular dichroism in photoelectron emission in the case of buried Co2FeAl0:5Si0:5 layers. The relatively large inelastic mean free path (up to 20 nm) of fast photoelectrons enables us to extend the HAXPES technique with electron-spin polarimetry and to develop spin analysis techniques for buried magnetic multilayers and interfaces.","" "Bi-quadratic interlayer exchange coupling in Co2MnSi/Ag/Co2MnSi pseudo spin-valve","Bi-quadratic interlayer exchange coupling in Co2MnSi/Ag/Co2MnSi pseudo spin-valve","Hari S. Goripati, Masamitsu Hayashi, T. Furubayashi, T. Taniguchi, H. Sukegawa, Y. K. Takahashi, K. Hono","Hari S. Goripati, Masamitsu Hayashi, T. Furubayashi, T. Taniguchi, H. Sukegawa, Y. K. Takahashi, K. Hono","Journal of Applied Physics","Journal of Applied Physics","110","12","123914","","2011-12-15","TRUE","","scientific_journal","eng","","10.1063/1.3671634","","Bi-quadratic interlayer exchange coupling is found below 100 K in a Co2MnSi/Ag/Co2MnSi current-perpendicular-to-plane pseudo spin valves. The bi-quadratic coupling constant J2 was estimated to be 0.30 erg/cm2 at 5 K and the strong temperature dependence of the coupling strength points its likely origin to the “loose spin” model. Application of current of 2107 A/ cm2 below 100 K leads to an increase in the magnetoresistance (MR), indicating current induced antiparallel alignment of the two magnetic layers. These results strongly suggest that the presence of the bi-quadratic interlayer exchange coupling causes the reduction of the magnetoresistance at low temperature and illustrates the importance of understanding the influence of interlayer exchange coupling on magnetization configura","" "Sophisticated Crystal Transformation of a Coordination Polymer into Mesoporous Monocrystalline Ti-Fe-Based Oxide with Room-Temperature Ferromagnetic Behavior","Sophisticated Crystal Transformation of a Coordination Polymer into Mesoporous Monocrystalline Ti-Fe-Based Oxide with Room-Temperature Ferromagnetic Behavior","Ming Hu, Alexei A. Belik, Hiroaki Sukegawa, Yoshihiro Nemoto, Masataka Imura, Yusuke Yamauchi ","Ming Hu, Alexei A. Belik, Hiroaki Sukegawa, Yoshihiro Nemoto, Masataka Imura, Yusuke Yamauchi ","Chemistry - An Asian Journal","Chemistry - An Asian Journal","6","12","3195","3199","2011-12-02","TRUE","","scientific_journal","eng","","10.1002/asia.201100509","","Recently, many efforts have been made for preparation of mesoporous crystalline materials. In general, during the framework crystallization, framework shrinkage is hard to avoid, which can cause collapse of the mesoporous structure. Kondo and Domen et al. have reported single-crystal particles of mixed transition metal oxide with a wormhole mesoporous structure by controlled two-step calcination.[5] Fine control of the calcination temperature is effective for successful crystallization with the retention of mesoporosity. Hard-templating strategy is another way;[6] this approach is widely applicable to the preparation of metal oxides, which are difficult to synthesize by conventional surfactant-templating pathways. Many kinds of mesoporous crystalline metal oxides (e.g., CoO,[7] Co3O4,[8] M","" "Size-Tunable Silicon/Iron Oxide Hybrid Nanoparticles with Fluorescence, Superparamagnetism, and Biocompatibility","蛍光、超常磁性、生体適合性を持ったサイズ可変Si/Fe酸化物ハイブリッドナノ粒子","Keisuke Sato, Shinobu Yokosuka, Yasunori Takigami, Kenji Hirakuri, Kouki Fujioka, Yoshinobu Manome, Hiroaki Sukegawa, Hideo Iwai, Naoki Fukata","Keisuke Sato, Shinobu Yokosuka, Yasunori Takigami, Kenji Hirakuri, Kouki Fujioka, Yoshinobu Manome, Hiroaki Sukegawa, Hideo Iwai, Naoki Fukata","Journal of the American Chemical Society","Journal of the American Chemical Society","133","46","18626","18633","2011-11-23","TRUE","","scientific_journal","eng","","10.1021/ja202466m","","Magnetic/fluorescent composite materials have become one of the most important tools in the imaging modality in vivo using magnetic resonance imaging (MRI) monitoring and fluorescence optical imaging. We report herein on a simplified procedure to synthesize hybrid nanoparticles (HNPs) that combine silicon and magnetic iron oxides consisting of magnetite (Fe3O4) and maghemite (γ-Fe2O3). Intriguingly, our unique synthetic approach can control magnetic and optical behaviors by reducing the particle size.","" "Correlation between symmetry-selective transport and spin-dependent resonant tunneling in fully epitaxial Cr/ultrathin-Fe/MgO/Fe(001) magnetic tunnel junctions","フルエピタキシャルCr/Fe/MgO/Crトンネル接合における対称性選択トンネル過程とスピン依存共鳴トンネル効果の相関","Tomohiko Niizeki, Hiroaki Sukegawa, Seiji Mitani, Nobuki Tezuka, Koichiro Inomata","Tomohiko Niizeki, Hiroaki Sukegawa, Seiji Mitani, Nobuki Tezuka, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","99","18","182508","","2011-10-31","TRUE","","scientific_journal","eng","","10.1063/1.3647578","","スピン依存共鳴トンネル効果は、新しいアーキテクチャの高集積MRAMに応用できる可能性があり、近年注目を集めている。本研究では、スピン依存共鳴トンネル効果に及ぼすsymmetry selective tunneling過程の影響を調べた。その結果、新しい知見としてsymmetry selective tunnelingと共鳴トンネル効果の間には明瞭な正の相関があり、スピン依存共鳴トンネル効果の応用には、symmetry selective tunnelingの効果の大きい単結晶(若しくは高配向)トンネルバリアの利用が必須であることが分かった。","" "Magnetic dichroism in angle-resolved hard x-ray photoemission from buried layers","Magnetic dichroism in angle-resolved hard x-ray photoemission from buried layers","Xeniya Kozina, Gerhard H. Fecher, Gregory Stryganyuk, Siham Ouardi, Benjamin Balke, Claudia Felser, Gerd Schönhense, Eiji Ikenaga, Takeharu Sugiyama, Naomi Kawamura, Motohiro Suzuki, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Keisuke Kobayashi","Xeniya Kozina, Gerhard H. Fecher, Gregory Stryganyuk, Siham Ouardi, Benjamin Balke, Claudia Felser, Gerd Schönhense, Eiji Ikenaga, Takeharu Sugiyama, Naomi Kawamura, Motohiro Suzuki, Tomoyuki Taira, Tetsuya Uemura, Masafumi Yamamoto, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Keisuke Kobayashi","Physical Review B","Physical Review B","84","5","","","2011-08-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.84.054449","","This work reports the measurement of magnetic dichroism in angular-resolved photoemission from in-plane magnetized buried thin films. The high bulk sensitivity of hard x-ray photoelectron spectroscopy (HAXPES) in combination with circularly polarized radiation enables the investigation of the magnetic properties of buried layers. HAXPES experiments with an excitation energy of 8 keV were performed on exchange-biased magnetic layers covered by thin oxide films. Two types of structures were investigated with the IrMn exchange-biasing layer either above or below the ferromagnetic layer: one with a CoFe layer on top and another with a Co2FeAl layer buried beneath the IrMn layer. A pronounced magnetic dichroism is found in the Co and Fe 2p states of both materials. ","" "Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface","Perpendicular magnetization of Co2FeAl full-Heusler alloy films induced by MgO interface","Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani, Koichiro Inomata","Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","98","24","242507","","2011-06-13","TRUE","","scientific_journal","eng","","10.1063/1.3600645","","The perpendicular magnetization of Co2FeAl (CFA) full-Heusler alloy films was achieved in the structures of CFA/MgO and MgO/CFA with the perpendicular magnetic anisotropy energy density (KU) of 2–3x10^6 erg/cm^3, which can be used as the perpendicular ferromagnetic electrodes of MgO-based magnetic tunnel junctions (MTJs) with high thermal stability at sub-50nm dimension. This letter 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 in MgO-based MTJ nanopillars with perpendicular full-Heusler alloy electrodes.","" "Spin Dynamics of B2 and L2 1 -Ordered Co 2 FeAl 0.5 Si 0.5 Heusler Alloy Films","Spin Dynamics of B2 and L21-Ordered Co2FeAl0.5Si0.5 Heusler Alloy Films","Ming Yi, Zhi-Feng Chen, Da-Xin Chen, Tian-Shu Lai, Shi-Ming Zhou","Ming Yi, Zhi-Feng Chen, Da-Xin Chen, Tian-Shu Lai, Shi-Ming Zhou","Chinese Physics Letters","Chinese Physics Letters","28","6","067501","","2011-06-01","TRUE","","scientific_journal","eng","","10.1088/0256-307x/28/6/067501","","Measurements of magnetization precession are performed for L21 and B2-ordered Co2FeAl0.5Si0.5 full Heusler alloy films using the time-resolved magneto-optical Kerr effect technique in the out-of-plan configuration. Dependence of the precession frequency on the external magnetic field can be fitted by the Landau-Lifshitz-Gilbert equation. The chirp parameters are close to each other for the L21 and B2 structures, and decrease with the external magnetic field increasing. The relaxation rate of the B2-ordered film is smaller than that of the L21 one.","" "Tunnel magnetoresistance in textured Co2FeAl/MgO/CoFe magnetic tunnel junctions on a Si/SiO2 amorphous substrate","Tunnel magnetoresistance in textured Co2FeAl/MgO/CoFe tunnel junctions on a Si/SiO2 amorphous substrate","Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani, Koichiro Inomata","Zhenchao Wen, Hiroaki Sukegawa, Seiji Mitani, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","98","19","192505","","2011-05-09","TRUE","","scientific_journal","eng","","10.1063/1.3587640","","Magnetic tunnel junctions with B2-ordered Co2FeAl full Heusler alloy as a ferromagnetic electrode were fabricated by sputtering on thermally oxidized Si/SiO2 amorphous substrates. A Co2FeAl/MgO/Co50Fe50 structure showed a highly 001-textured structure and the tunneling magnetoresistance ratio of 166% at room temperature and 252% at 48 K were achieved. The temperature dependence of TMR can be fitted with spin wave excitation model, and the bias voltage dependence of differential conductance demonstrated that the high TMR was mainly contributed by coherent tunneling. This work suggests the B2-Co2FeAl is one of the promising candidates for practical spintronic applications.","" "Crystallinity and Transport Properties in Fe/MgAl2O4/Fe(001) Epitaxial Magnetic Tunnel Junctions","エピタキシャルFe/MgAl2O4/Fe(001)強磁性トンネル接合における結晶性と伝導特性","介川 裕章, 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, 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","Journal of the Magnetics Society of Japan","Journal of the Magnetics Society of Japan","35","3","254","259","2011-04-28","TRUE","","scientific_journal","jpn","","10.3379/msjmag.1104r011","","","We investigated in detail the crystallinity and transport properties of fully epitaxial Fe(001)/spinel MgAl2O4(001)/Fe(001) magnetic tunnel junctions (MTJs). We found that high (001) orientation (< 0.20°) and an extremely flat surface (averaged roughness ~ 0.09 nm) were achieved in the optimized Fe/MgAl2O4/Fe MTJs exhibiting tunnel magnetoresistance (TMR) of more than 100% as well as excellent bias-voltage dependence. The misfit dislocation density of the MgAl2O4/Fe interface was determined to be precisely 5 × 10−2 nm−1. In addition, post-annealing in the preparation process has a significant influence on TMR and its bias-voltage dependence in Fe/MgAl2O4/Fe MTJs, suggesting that the crystallinity of the MgAl2O4 barrier interfaces was effectively improved by postannealing o" "Fully epitaxial Fe/MgO/Fe(001) junctions with nonmagnetic metal layer insertion","非磁性金属中間層を挿入したFe/MgO/Fe(001)フルエピタキシャル接合","T. Niizeki, S. Mitani, H. Sukegawa, S. Kasai, K. Inomata","T. Niizeki, S. Mitani, H. Sukegawa, S. Kasai, K. Inomata","Journal of Applied Physics","Journal of Applied Physics","109","7","07C726","","2011-04-01","TRUE","","scientific_journal","eng","","10.1063/1.3555086","","MRAM等への応用を目指した新しいスピントロニクス素子として、非磁性中間層を挿入したFe/MgO/Feトンネル接合を作製した。非磁性中間層の量子井戸準位に起因する磁気抵抗効果と素子抵抗の層厚に対する振動的変化を観測した。スイッチング機能を有する強磁性トンネル接合素子への展開が期待される成果である。","" "Effect of annealing on Co2FeAl0.5Si0.5thin films: A magneto-optical and x-ray absorption study","Effect of annealing on Co2FeAl0.5Si0.5 thin films: A magneto-optical and x-ray absorption study","Simon Trudel, Georg Wolf, Jaroslav Hamrle, Burkard Hillebrands, Peter Klaer, Michael Kallmayer, Hans-Joachim Elmers, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata","Simon Trudel, Georg Wolf, Jaroslav Hamrle, Burkard Hillebrands, Peter Klaer, Michael Kallmayer, Hans-Joachim Elmers, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata","Physical Review B","Physical Review B","83","10","","","2011-03-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.83.104412","","A series of Al and MgO-capped Co2FeAl0.5Si0.5 epitaxial thin films grown on MgO with various levels of L21 ordering was obtained by in situ annealing. The films were studied by means of x-ray absorption spectroscopy, x-ray magnetic circular dichroism (XMCD), magneto-optical Kerr effect magnetometry, and Brillouin light scattering. We find the anisotropy constants decrease, while the spin wave stiffness increases as the samples are annealed to higher temperatures. The magnetization as determined by Brillouin light scattering reveals a maximum value at intermediate annealing temperatures. Surprisingly, the orbital-to-spin-moment ratio is essentially stable through the sample series and does not change upon annealing, despite the observed changes in anisotropy and exchange.","" "Current-perpendicular-to-plane spin valves with a Co2Mn(Ga0.5Sn0.5) Heusler alloy","Co2Mn(Ga0.5Sn0.5)ホイスラー合金を用いたCPPスピンバルブ","N. Hase, B. S. D. Ch. S. Varaprasad, T. M. Nakatani, H. Sukegawa, S. Kasai, Y. K. Takahashi, T. Furubayashi, K. Hono","N. Hase, B. S. D. Ch. S. Varaprasad, T. M. Nakatani, H. Sukegawa, S. Kasai, Y. K. Takahashi, T. Furubayashi, K. Hono","Journal of Applied Physics","Journal of Applied Physics","108","9","093916","","2010-11-01","TRUE","","scientific_journal","eng","","10.1063/1.3503869","","Current-perpendicular-to-plane spin valves (SV) with a new Heusler alloy of Co2Mn(Ga0.5Sn0.5) (CMGS) as magnetic layers and a Ag spacer have been investigated. Magnetoresistance (MR) values of 8.8% and 17.2%, and resistance change-area product (ΔRA) of 4.0 mΩμm2 and 6.5 mΩμm2 were measured at 300 K and 12 K, respectively. Transmission electron microscopy observations have revealed that the CMGS magnetic layer was ordered to the B2 structure for the SV annealed at 400oC. Higher annealing temperature led to the degradation of the multilayer structure, resulting in lower MR and ΔRA values regardless of the L21 structure of the CMGS layer. This suggests that MR properties may be enhanced further if the thermal stability of the multilayer structure is improved.","" "Aerosol-Assisted Synthesis of Thiol-Functionalized Mesoporous Silica Spheres with Fe3O4 Nanoparticles","Aerosol-Assisted Synthesis of Thiol-Functionalized Mesoporous Silica Spheres with Fe3O4 Nanoparticles","Norihiro Suzuki, Prashant Gupta, Hiroaki Sukegawa, Kouichiro Inomata, Satoru Inoue, Yusuke Yamauchi","Norihiro Suzuki, Prashant Gupta, Hiroaki Sukegawa, Kouichiro Inomata, Satoru Inoue, Yusuke Yamauchi","Journal of Nanoscience and Nanotechnology","Journal of Nanoscience and Nanotechnology","10","10","6612","6617","2010-10-01","TRUE","","scientific_journal","eng","","10.1166/jnn.2010.2546","","We report aerosol-assisted synthesis of mesoporous thiol-functionalized mesoporous silica spheres with Fe3O4 nanoparticles.","" "Temperature dependence of tunneling magnetoresistance in epitaxial magnetic tunnel junctions using aCo2FeAlHeusler alloy electrode","Temperature dependence of tunneling magnetoresistance in epitaxial magnetic tunnel junctions using aCo2FeAlHeusler alloy electrode","Wenhong Wang, Hiroaki Sukegawa, Koichiro Inomata","Wenhong Wang, Hiroaki Sukegawa, Koichiro Inomata","Physical Review B","Physical Review B","82","9","","","2010-09-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.82.092402","","Spin-valve-type epitaxial magnetic tunnel junctions (MTJs) consisting of a full-Heusler alloy Co2FeAl (CFA) and a MgO tunnel barrier were fabricated on a single-crystal MgO(001) substrate using sputtering method for all the layers. Experimental temperature-dependent tunnel magnetoresistance in the MTJs was revealed to be fitted well using spin wave excitation model for tunneling spin polarization, P(T)=P0(1− alpha x T^3/2) up to room temperature, where P0 is the spin polarization at 0 K and alpha is a fitting parameter. The determined P and alpha are shown to be significantly different between bottom and top CFA electrodes facing a MgO barrier. It is demonstrated that the bottom CFA deposited on a Cr buffer has a low alpha and behaves as a half-metal with P~1 in terms of the delta1 s","" "Perpendicular Magnetic Anisotropy of Co2FeAl/Pt Multilayers for Spintronic Devices","Perpendicular Magnetic Anisotropy of Co2FeAl/Pt Multilayers for Spintronic Devices","Wenhong Wang, Hiroaki Sukegawa, Koichiro Inomata","Wenhong Wang, Hiroaki Sukegawa, Koichiro Inomata","Applied Physics Express","Applied Physics Express","3","9","093002","","2010-09-01","TRUE","","scientific_journal","eng","","10.1143/apex.3.093002","","We report on the experimental realization of perpendicular magnetic anisotropy in Co2FeAl/Pt multilayers, which were prepared on Pt buffered MgO(001) substrates by magnetron sputtering. It was found that the perpendicular magnetic anisotropy is related to the number of periods N of the multilayers and also the thickness of Co2FeAl. The perpendicular-anisotropy energy density Ku is estimated to be 1.45x10^6 erg/cm^3 at room temperature, which is comparable to that of the Co/(Pd,Pt) multilayers. This suggests that Co2FeAl/Pt system presented here will be a good candidate for use as the highly spin polarized ferromagnetic electrodes in MgO-based tunnel junctions with perpendicular magnetization.","" "Temperature dependence of x-ray absorption spectra in the ferromagnetic Heusler alloysMn2VAlandCo2FeAl","Temperature dependence of x-ray absorption spectra in the ferromagnetic Heusler alloysMn2VAlandCo2FeAl","P. Klaer, E. Arbelo Jorge, M. Jourdan, W. H. Wang, H. Sukegawa, K. Inomata, H. J. Elmers","P. Klaer, E. Arbelo Jorge, M. Jourdan, W. H. Wang, H. Sukegawa, K. Inomata, H. J. Elmers","Physical Review B","Physical Review B","82","2","","","2010-07-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.82.024418","","We investigate the temperature dependence of the spin-resolved unoccupied density of states (DOS) in ferromagnetic Co2FeAl and ferrimagnetic Mn2VAl epitaxial films on MgO(100) using x-ray magnetic circular dichroism. We observe an unexpected strong temperature dependence of the DOS beyond the change expected from the Fermi distribution function. An increase in spectral weight is observed for majority states below the Fermi energy in the case of Mn2VAl and for minority states above the Fermi energy in the case of Co2FeAl. Reduced atomic order near the interface suppresses the unexpected temperature dependence of the DOS for Mn2VAl.","" "Structure and transport properties of current-perpendicular-to-plane spin valves using Co2FeAl0.5Si0.5 and Co2MnSi Heusler alloy electrodes","Co2FeAl0.5Si0.5 及び Co2MnSi ホイスラー合金を用いたCPPスピンバルブの構造と輸送特性","T. Furubayashi, K. Kodama, T. M. Nakatani, H. Sukegawa, Y. K. Takahashi, K. Inomata, K. Hono","T. Furubayashi, K. Kodama, T. M. Nakatani, H. Sukegawa, Y. K. Takahashi, K. Inomata, K. Hono","Journal of Applied Physics","Journal of Applied Physics","107","11","113917","","2010-06-01","TRUE","","scientific_journal","eng","","10.1063/1.3431530","","We report the structure and transport properties of CPP SV with Co2FeAl0.5Si0.5 (CFAS) or Co2MnSi (CMS) Heusler alloy magnetic layers and an Ag or Cu spacer layer. A multilayer stack of sub/Cr/Ag/Heusler/(Ag or Cu)/Heusler/Co75Fe25/Ir22Mn78/Ru was deposited on a MgO(001) single crystalline substrate by magnetron sputtering. TEM observations showed epitaxial growth from the substrate to the top Heusler layer. The CPP SV with a CFAS/Ag/CFAS trilayer showed relatively large magnetoresistance ratios of 12% at room temperature and 31% at 12 K, with monotonous temperature dependence. However, the MR values of the SV with the CMS/Ag/CMS trilayer showed a different temperature dependence with a maximum value of 22% at 100 K. This might be related to the 90° couplings between the two CMS layers.","" "Bulk and interfacial scatterings in current-perpendicular-to-plane giant magnetoresistance with Co2Fe(Al0.5Si0.5) Heusler alloy layers and Ag spacer","ホイスラー合金Co2Fe(Al0.5Si0.5)とAgスペーサーを用いたCPP-GMRにおけるバルク散乱と界面散乱","T. M. Nakatani, T. Furubayashi, S. Kasai, H. Sukegawa, Y. K. Takahashi, S. Mitani, K. Hono","T. M. Nakatani, T. Furubayashi, S. Kasai, H. Sukegawa, Y. K. Takahashi, S. Mitani, K. Hono","Applied Physics Letters","Applied Physics Letters","96","21","212501","","2010-05-24","TRUE","","scientific_journal","eng","","10.1063/1.3432070","","超高密度磁気記録用センサーとしての応用が期待されるホイスラー合金CPP-GMR素子について,そのCPP-GMRの起源を,バルク散乱と界面散乱に分離して議論した.","" "Tunnel magnetoresistance with improved bias voltage dependence in lattice-matched Fe/spinel MgAl2O4/Fe(001) junctions","Tunnel magnetoresistance with improved bias voltage dependence in lattice-matched Fe/spinel MgAl2O4/Fe(001) junctions","Hiroaki Sukegawa, Huixin Xiu, Tadakatsu Ohkubo, Takao Furubayashi, Tomohiko Niizeki, Wenhong Wang, Shinya Kasai, Seiji Mitani, Koichiro Inomata, Kazuhiro Hono","Hiroaki Sukegawa, Huixin Xiu, Tadakatsu Ohkubo, Takao Furubayashi, Tomohiko Niizeki, Wenhong Wang, Shinya Kasai, Seiji Mitani, Koichiro Inomata, Kazuhiro Hono","Applied Physics Letters","Applied Physics Letters","96","21","212505","","2010-05-24","TRUE","","scientific_journal","eng","","10.1063/1.3441409","","We fabricated fully epitaxial Fe/MgAl2O4 /Fe(001) magnetic tunnel junctions using plasma oxidation of an Mg/Al bilayer. The MgAl2O4 showed a (001)-oriented spinel-type structure, and there were few misfit dislocations at the interfaces between the MgAl2O4 and the two Fe layers due to a small lattice mismatch (~1%). Tunnel magnetoresistance (TMR) ratios up to 117% (165%) were obtained at room temperature (15 K). The bias voltage for one-half of the zero-bias TMR ratio (Vhalf) was relatively large, ranging from 1.0 to 1.3 V at room temperature, which is attributed to the small misfit dislocation density.","" "Interfacial structure and magnetic properties of Co2FeAl0.5Si0.5/MgO heterostructures","Interfacial structure and magnetic properties of Co2FeAl0.5Si0.5/MgO heterostructures","Sameh S. A. Hassan, Yongbing Xu, Atsufumi Hirohata, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Gerrit van der Laan","Sameh S. A. Hassan, Yongbing Xu, Atsufumi Hirohata, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Gerrit van der Laan","Journal of Applied Physics","Journal of Applied Physics","107","10","103919","","2010-05-15","TRUE","","scientific_journal","eng","","10.1063/1.3371694","","The interfacial properties of the Co2FeAl0.5Si0.5 /MgO based magnetic tunnel junction have been investigated using x ray absorption spectroscopy (XAS), angle resolved x ray photoelectron spectroscopy (ARXPS), x ray magnetic circular dichroism (XMCD), and element-specific hysteresis loops. The XAS demonstrates a multiplet structure at the Co L3 edge which could be attributed to the formation of CoO at the interface due to the high annealing temperature. The XMCD sum-rule analysis and the element-specific hysteresis loops show a higher magnetic moment, a change in the loop shape, and an increase in the Co coercive field when probing more close to the interface layer. The chemical and structural disorder at the interface has been further revealed by the ARXPS measurements.","" "Coherent tunneling and giant tunneling magnetoresistance inCo2FeAl/MgO/CoFemagnetic tunneling junctions","Coherent tunneling and giant tunneling magnetoresistance inCo2FeAl/MgO/CoFemagnetic tunneling junctions","Wenhong Wang, Enke Liu, Masaya Kodzuka, Hiroaki Sukegawa, Marec Wojcik, Eva Jedryka, G. H. Wu, Koichiro Inomata, Seiji Mitani, Kazuhiro Hono","Wenhong Wang, Enke Liu, Masaya Kodzuka, Hiroaki Sukegawa, Marec Wojcik, Eva Jedryka, G. H. Wu, Koichiro Inomata, Seiji Mitani, Kazuhiro Hono","Physical Review B","Physical Review B","81","14","","","2010-04-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.81.140402","","Spin-dependent coherent tunneling has been experimentally observed in high-quality sputtered-deposited Co2FeAl/MgO/CoFe epitaxial magnetic tunneling junctions (MTJs). Consequently, the microfabricated MTJs manifest a very large tunnel magnetoresistance (TMR) at room temperature and an unexpectedly TMR oscillation as a function of MgO barrier thickness. First-principles electronic band calculations confirm the pronounced coherent tunneling effect and are in good agreement with the experimental data. The present work demonstrates the importance of coherent tunneling for large TMR with Heusler alloys","" "Spin-transfer switching in an epitaxial spin-valve nanopillar with a full-Heusler Co2FeAl0.5Si0.5 alloy","Spin-transfer switching in an epitaxial spin-valve nanopillar with a full-Heusler Co2FeAl0.5Si0.5 alloy","Hiroaki Sukegawa, Shinya Kasai, Takao Furubayashi, Seiji Mitani, Koichiro Inomata","Hiroaki Sukegawa, Shinya Kasai, Takao Furubayashi, Seiji Mitani, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","96","4","042508","","2010-01-25","TRUE","","scientific_journal","eng","","10.1063/1.3297879","","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 (~106 A/cm2 in current density). Statistical analysis based on a thermal activation model revealed an averaged critical current density (Jc0) of 9.3 × 106 A/cm2 with a thermal stability factor (KV/kBT) of ~40.","" "A New Spin-Functional Metal–Oxide–Semiconductor Field-Effect Transistor Based on Magnetic Tunnel Junction Technology: Pseudo-Spin-MOSFET","A New Spin-Functional Metal–Oxide–Semiconductor Field-Effect Transistor Based on Magnetic Tunnel Junction Technology: Pseudo-Spin-MOSFET","Yusuke Shuto, Ryosho Nakane, Wenhong Wang, Hiroaki Sukegawa, Shuu'ichirou Yamamoto, Masaaki Tanaka, Koichiro Inomata, Satoshi Sugahara","Yusuke Shuto, Ryosho Nakane, Wenhong Wang, Hiroaki Sukegawa, Shuu'ichirou Yamamoto, Masaaki Tanaka, Koichiro Inomata, Satoshi Sugahara","Applied Physics Express","Applied Physics Express","3","1","013003","","2010-01-01","TRUE","","scientific_journal","eng","","10.1143/apex.3.013003","","We fabricated and characterized a new spin-functional metal–oxide–semiconductor field-effect transistor (MOSFET) referred to as a pseudo-spin-MOSFET (PS-MOSFET). The PS-MOSFET is a circuit using an ordinary MOSFET and magnetic tunnel junction (MTJ) for reproducing functions of spin-transistors. Device integration techniques for a bottom gate MOSFET using a silicon-on-insulator (SOI) substrate and for an MTJ with a full-Heusler alloy electrode and MgO tunnel barrier were developed. The fabricated PS-MOSFET exhibited high and low transconductance controlled by the magnetization configurations of the MTJ at room temperature. This is the first observation of spin-transistor operations for spinfunctional MOSFETs.","" "Giant tunneling magnetoresistance up to 330% at room temperature in sputter deposited Co2FeAl/MgO/CoFe magnetic tunnel junctions","Giant tunneling magnetoresistance up to 330% at room temperature in sputter deposited Co2FeAl/MgO/CoFe magnetic tunnel junctions","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Seiji Mitani, Koichiro Inomata","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Seiji Mitani, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","95","18","182502","","2009-11-02","TRUE","","scientific_journal","eng","","10.1063/1.3258069","","Magnetoresistance ratio up to 330% at room temperature (700% at 10 K) has been obtained in a spin-valve-type magnetic tunnel junction (MTJ) consisting of a full-Heusler alloy Co2FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO (001) substrate by sputtering method. The output voltage of the MTJ at one-half of the zero-bias value was found to be as high as 425 mV, which is the largest reported to date in MTJs using Heusler alloy electrodes.","" "Ferromagnetic Mesostructured Alloys: Design of Ordered Mesostructured Alloys with Multicomponent Metals from Lyotropic Liquid Crystals","Ferromagnetic Mesostructured Alloys: Design of Ordered Mesostructured Alloys with Multicomponent Metals from Lyotropic Liquid Crystals","Yusuke Yamauchi, Masaki Komatsu, Minekazu Fuziwara, Yoshihiro Nemoto, Keisuke Sato, Tokihiko Yokoshima, Hiroaki Sukegawa, Kouichiro Inomata, Kazuyuki Kuroda","Yusuke Yamauchi, Masaki Komatsu, Minekazu Fuziwara, Yoshihiro Nemoto, Keisuke Sato, Tokihiko Yokoshima, Hiroaki Sukegawa, Kouichiro Inomata, Kazuyuki Kuroda","Angewandte Chemie International Edition","Angewandte Chemie International Edition","48","42","7792","7797","2009-10-05","TRUE","","scientific_journal","eng","","10.1002/anie.200902934","","We prepare ferromagnetic mesostructured alloys from lyotropic liquid crystals.","" "Demonstration of Half-Metallicity in Fermi-Level-Tuned Heusler AlloyCo2FeAl0.5Si0.5at Room Temperature","Demonstration of Half-Metallicity in Fermi-Level-Tuned Heusler AlloyCo2FeAl0.5Si0.5at Room Temperature","R. Shan, H. Sukegawa, W. H. Wang, M. Kodzuka, T. Furubayashi, T. Ohkubo, S. Mitani, K. Inomata, K. Hono","R. Shan, H. Sukegawa, W. H. Wang, M. Kodzuka, T. Furubayashi, T. Ohkubo, S. Mitani, K. Inomata, K. Hono","Physical Review Letters","Physical Review Letters","102","24","","","2009-06-01","TRUE","","scientific_journal","eng","","10.1103/physrevlett.102.246601","","Fermi level tuning has been successfully demonstrated in Co-based full-Heusler alloy Co2FeAl0.5Si0.5 (CFAS). The half-metallic band gap of CFAS was proved by the behavior of differential conductance of CFAS/MgAl2Ox/CoFe magnetic tunneling junctions with an unexplored crystalline MgAl2Ox barrier. CFAS exhibits the highest effective spin polarization (Peff ) at 300 K and the weakest temperature dependence of Peff among all known half metals. Further study shows that Peff of CFAS decays with increasing temperature (T) following T3=2 law perfectly, which indicates that the depolarization of CFAS is determined by spin wave excitation only.","" "Tunnel Magnetoresistance in Full-Heusler Co2FeAl0.5Si0.5-Based Magnetic Tunnel Junctions","フルホイスラーCo2FeAl0.5Si0.5合金を有する強磁性トンネル接合の素子構造とトンネル磁気抵抗効果","介川 裕章, Wenhong Wang, Rong Shan, 猪俣 浩一郎","介川 裕章, Wenhong Wang, Rong Shan, 猪俣 浩一郎","Journal of the Magnetics Society of Japan","Journal of the Magnetics Society of Japan","33","3","256","261","2009-05-21","TRUE","","scientific_journal","jpn","","10.3379/msjmag.0903re8037","","","We fabricated fully epitaxial magnetic tunnel junctions (MTJs) with full-Heusler Co2FeAl0.5Si0.5 (CFAS) electrodes using the sputtering method. We changed the MgO barrier thickness, the thickness of an Mg layer inserted between the CFAS and MgO layers, and a post-annealing process for CFAS layers in order to obtain conditions necessary for achieving a high tunnel magnetoresistance (TMR) ratio. We found that both the MgO barrier thickness and the post-annealing temperature directly influenced the TMR ratio while the thin Mg layer insertion did not. " "Spin-polarized tunneling spectroscopy of fully epitaxial magnetic tunnel junctions usingCo2FeAl0.5Si0.5Heusler alloy electrodes","Spin-polarized tunneling spectroscopy of fully epitaxial magnetic tunnel junctions usingCo2FeAl0.5Si0.5Heusler alloy electrodes","Hiroaki Sukegawa, Wenhong Wang, Rong Shan, Tomoya Nakatani, Koichiro Inomata, Kazuhiro Hono","Hiroaki Sukegawa, Wenhong Wang, Rong Shan, Tomoya Nakatani, Koichiro Inomata, Kazuhiro Hono","Physical Review B","Physical Review B","79","18","","","2009-05-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.79.184418","","Spin-dependent tunneling spectroscopy has been studied in fully epitaxial magnetic tunnel junctions with full-Heusler Co2FeAl0.5Si0.5 (CFAS) alloys. We fabricated CFAS/MgO/CFAS structures with L21- and B2-ordered CFAS layers and measured the bias voltage dependence of differential conductance G. We found for L21-CFAS/MgO/L21-CFAS structure symmetrical conductance curves with respect to polarity of the bias voltage for parallel (P) and antiparallel (AP) magnetization configurations and two characteristic crossovers in G between P and AP accompanied with a flat feature within  0.6 V in GP. On the other hand, only one crossover was observed at a negative-bias voltage for L21-CFAS/MgO/B2-CFAS structure. The direct tunneling that reflects the specific spin-dependent density of states of the ha","" "Hard x-ray photoelectron spectroscopy of buried Heusler compounds","Hard x-ray photoelectron spectroscopy of buried Heusler compounds","Siham Ouardi, Benjamin Balke, Andrei Gloskovskii, Gerhard H Fecher, Claudia Felser, Gerd Schönhense, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Yoshiyuki Yamashita, Hideki Yoshikawa, Shigenori Ueda, Keisuke Kobayashi","Siham Ouardi, Benjamin Balke, Andrei Gloskovskii, Gerhard H Fecher, Claudia Felser, Gerd Schönhense, Takayuki Ishikawa, Tetsuya Uemura, Masafumi Yamamoto, Hiroaki Sukegawa, Wenhong Wang, Koichiro Inomata, Yoshiyuki Yamashita, Hideki Yoshikawa, Shigenori Ueda, Keisuke Kobayashi","Journal of Physics D: Applied Physics","Journal of Physics D: Applied Physics","42","8","084010","","2009-04-21","TRUE","","scientific_journal","eng","","10.1088/0022-3727/42/8/084010","","This work reports on high energy photoelectron spectroscopy from the valence band of buried Heusler thin films excited by photons of about 6 keV energy. The high resolution measurements of the valence band close to Fermi energy indicate a very large mean free path of electrons through the insulating layer. ","" "Structure and spin polarization of outermost surface of the Co2FeAl0.5Si0.5 full-Heusler alloy studied by spin-polarized ion-scattering spectroscopy","Structure and spin polarization of outermost surface of the Co2FeAl0.5Si0.5 full-Heusler alloy studied by spin-polarized ion-scattering spectroscopy","T. T. Suzuki, H. Sukegawa, K. Inomata","T. T. Suzuki, H. Sukegawa, K. Inomata","Physical Review B","Physical Review B","79","4","","","2009-01-01","TRUE","","scientific_journal","eng","","10.1103/physrevb.79.045423","","The outermost surfaces of epitaxial full-Heusler Co2FeAl0.5Si0.5 CFAS films on MgO 001 substrates were investigated using spin-polarized ion-scattering spectroscopy. It was found that the CFAS surface was terminated by an Fe-Al-Si layer with substitution of Fe with Al and/or Si. The spin polarization of the outermost surface was detected for the first time among Heusler alloys. It was found that the spin polarization of Al and/or Si atoms in the topmost layer was significantly lower than that of Co atoms in the second layer. It was also found that the polarity of the spin polarization at the Fermi level on the outermost surface was opposite to majority spins. A possible application of SP-ISS in the development of magnetoresistance materials is suggested.","" "Large tunnel magnetoresistance in Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunneling junctions prepared on thermally oxidized Si substrates with MgO buffer","Large tunnel magnetoresistance in Co2FeAl0.5Si0.5/MgO/Co2FeAl0.5Si0.5 magnetic tunneling junctions prepared on thermally oxidized Si substrates with MgO buffer","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Koichiro Inomata","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","93","18","182504","","2008-11-03","TRUE","","scientific_journal","eng","","10.1063/1.3020300","","Magnetic tunnel junction (MTJs) using polycrystalline Co2FeAl0.5Si0.5 (CFAS) electrodes with an MgO tunnel barrier were fabricated onto thermally oxidized Si substrates. Highly (001)-oriented and B2-ordered CFAS electrodes were obtained by optimizing growth conditions and post-annealing temperature. The microfabricated MTJs exhibited relatively high tunnel magnetoresistance (TMR) ratios of 125 % at room temperature and 196 % at 7 K. The large TMR obtained using oxidized Si substrates indicates that CFAS is promising for the practical applications.","" "Current-perpendicular-to-plane giant magnetoresistance in spin-valve structures using epitaxial Co2FeAl0.5Si0.5 /Ag/ Co2FeAl0.5S","Co2FeAl0.5Si0.5 /Ag/ Co2FeAl0.5Si0.5 エピタキシャル3層膜を用いた面直電流巨大磁気抵抗効果","T. Furubayashi, K. Kodama, H. Sukegawa, Y. K. Takahashi, K. Inomata, K. Hono","T. Furubayashi, K. Kodama, H. Sukegawa, Y. K. Takahashi, K. Inomata, K. Hono","Applied Physics Letters","Applied Physics Letters","93","12","122507","","2008-09-22","TRUE","","scientific_journal","eng","","10.1063/1.2990647","","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.","" "Fabrication of fully epitaxial magnetic tunnel junctions using L21-ordered Co2FeAl0.5Si0.5 electrodes and their tunneling magnet","Fabrication of fully epitaxial magnetic tunnel junctions using L21-ordered Co2FeAl0.5Si0.5 electrodes and their tunneling magnet","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Koichiro Inomata","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","93","12","122506","","2008-09-22","TRUE","","scientific_journal","eng","","10.1063/1.2988649","","Magnetic tunnel junctions (MTJs) using L21-ordered full-Heusler Co2FeAl0.5Si0.5 (CFAS) electrodes and an MgO tunnel barrier were prepared on MgO-buffered MgO (001) substrates by sputtering method. In situ and ex situ structural characterization confirms that the stacking structure of CFAS/MgO/CFAS is fully epitaxial, with smooth interfaces throughout. The microfabricated MTJs exhibited relatively high tunnel magnetoresistance ratios of 150 % at room temperature and 312 % at 7 K. We observed a symmetrical crossover point from the bias voltage dependence of differential conductance between parallel and antiparallel magnetization configurations and also a flat behavior in the parallel conductance.","" "Preparation and characterization of highly L21-ordered full-Heusler alloy Co2FeAl0.5Si0.5 thin films for spintronics device applications","Preparation and characterization of highly L21-ordered full-Heusler alloy Co2FeAl0.5Si0.5 thin films for spintronics device applications","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Takao Furubayashi, Koichiro Inomata","Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Takao Furubayashi, Koichiro Inomata","Applied Physics Letters","Applied Physics Letters","92","22","221912","","2008-06-02","TRUE","","scientific_journal","eng","","10.1063/1.2940595","","We report the investigation of structure and magnetic properties of full-Heusler alloy Co2FeAl0.5Si0.5 (CFAS) thin films grown on MgO-buffered MgO (001) substrates through magnetron sputtering. It was found that single-crystal CFAS thin films with high degree of L21 ordering and sufficiently flat surface could be obtained after post-deposition annealing. All the films show a distinct uniaxial magnetic anisotropy with the easy axis of magnetization along the in-plane [110] direction. These results indicate that the use of the MgO-buffer for CFAS is a promising approach for achieving a higher tunnel magnetoresistance ratio, and thus for spintronics device applications. ",""