Multi-state electromagnetic phase modulations in NiCo2O4 through cation disorder and hydrogenation

Abstract

One focal challenge in engineering low-power and scalable all-oxide spintronic devices lies in exploring ferromagnetic oxide material with perpendicular magnetic anisotropy (PMA) and electronic conductivity while exhibiting tunable spin states. Targeting this need, spinel nickel cobaltite (NiCo2O4, NCO), featured by room-temperature ferrimagnetically metallic ground state with strong PMA, emerges as a promising candidate in the field of oxide spintronics. The cation distribution disorder inherent to NCO renders competing electromagnetic states and abnormal sign reversal of anomalous Hall effect (AHE), introducing an additional freedom to adjust electromagnetic transports. Here, we unveil multi-state electromagnetic phase modulations in NCO system through controllable cation disorder and proton evolution, extensively expanding electromagnetic phase diagram. The cation disorder in NCO tunable by growth temperature is identified as a critical control parameter for kinetically adjusting the proton evolution, giving rise to intermediate hydrogenated states with chemical stability. Hydrogen incorporation reversibly drives structural transformation and electromagnetic state evolutions in NCO, with rich spin-dependent correlated physics uncovered by combining the AHE scaling relation and synchrotron-based spectroscopy. Our work not only establishes NCO as a versatile platform for discovering spin-dependent physical functionality but also extends the horizons in materials design for state-of-the-art spintronic devices harnessing magneto-ionic control and inherent cation disorder.

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