Hydrogen anion as a strong magnetic mediator for obtaining high-temperature ferromagnetic semiconductors: The case of hydride double perovskites

Realizing ferromagnetic (FM) semiconductors with Curie temperatures (${T}_{c}$) above 300 K is highly desirable for spintronics but remains a big challenge. Up to now, the oxide double perovskite ${\mathrm{La}}_{2}{\mathrm{NiMnO}}_{6}$ is regarded as one of the most promising FM semiconductors, where the near-${180}^{\ensuremath{\circ}}$ strong superexchange interaction brings its ${T}_{c}$ up to 280 K, but it is still below room temperature. Here, we propose that, by using ${\mathrm{H}}^{\ensuremath{-}}$ instead of ${\mathrm{O}}^{2\ensuremath{-}}$ as magnetic mediator, the resulted perfect ${180}^{\ensuremath{\circ}}$ bond angle and short interaction distance between magnetic ions can notably raise the ${T}_{c}$ beyond 300 K. The idea is verified by theoretically designing a class of thermodynamically stable hydride double perovskites ${\mathrm{A}}_{2}{\mathrm{NiVH}}_{6} (\mathrm{A}=\mathrm{Na},\mathrm{K},\mathrm{Rb},\mathrm{Cs})$ with ferromagnetic ${T}_{c}$ up to 789 K. Moreover, the ${\mathrm{A}}_{2}{\mathrm{NiVH}}_{6}$ are identified as intriguing bipolar magnetic semiconductors with the carrier's spin orientation readily reversible by electrical gating. In addition, the possible Ni/V disorder further changes ${\mathrm{A}}_{2}{\mathrm{NiVH}}_{6}$ to be compensated ferrimagnetic semiconductors with vanishing magnetization, which may have unique advantages in antiferromagnetic spintronics.