Content 1 : The exchange-bias effect is an important magnetic phenomenon used in magnetic recording and spintronic devices. It is commonly realized in multilayer structures combining ferromagnetic and antiferromagnetic materials, but their fabrication can be complex, creating demand for bulk materials with alternative exchange-bias mechanisms. We have synthesized a bulk magnetic material that exhibits a large exchange-bias effect after cooling in only a small magnetic field. Our results suggest that spin-orbit coupling plays an important role and that the effect may arise from a mechanism fundamentally different from that in conventional interface-based systems. We are now working to clarify this mechanism and to develop new exchange-bias materials based on the resulting design principles.

Content 2: Metastable structures produced by high-pressure synthesis can retain atomic arrangements and free energy that are inaccessible in conventional thermodynamically stable phases. In the high-density oxide Ba4Ru3O12, we discovered an irreversible giant lattice expansion of approximately 4.4% caused by the rearrangement of ruthenium atoms and the release of structural frustration upon heating. This behavior is contrary to the conventional expectation that a high-density phase synthesized under pressure should contract or decompose at ambient pressure. The result demonstrates that free energy stored in a metastable structure can be converted into a macroscopic lattice response through atomic rearrangement. We are extending this concept toward new materials design that treats metastable structures as functional resources.