Hydrogen-Driven Ferromagnetic Insulator in Cobalt Perovskite above Room Temperature

Transition-metal oxyhydrides, composed of oxides and unique hydride anions, are rare and remarkable materials with significant potential applications in catalysis, battery technology, hydrogen storage, and photocatalysis. The addition of one electron to hydrogen imparts a bipolar nature and enhances its electronegativity, facilitating the formation of metallic, covalent, and ionic bonds in these transition-metal oxyhydrides. By utilizing topotactic reduction techniques, we successfully incorporated hydrogen into LaCoO₃ thin films, transforming them into H-LaCoO_2.5. Scanning transmission electron microscopy (STEM) images reveal that the lattice of H-LaCoO_2.5 contracts compared to that of LaCoO_2.5. Density functional theory (DFT) calculations suggest that the incorporated hydrogen atoms form hydride anions and occupy the oxygen vacancy sites. This unique phase exhibits ultrahigh-temperature ferromagnetic insulating behavior, with a Curie temperature exceeding 400 K and a saturation magnetization of 0.47 μ_B/Co at 380 K. Our work provides a novel platform for the development of energy-efficient room-temperature spintronic devices.