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-${180}^{\circ }$ strong superexchange interaction brings its $T_c$ up to 280 K, but it is still below room temperature. Here, we propose that, by using ${\mathrm{H}}^{-}$ instead of ${\mathrm{O}}^{2-}$ as magnetic mediator, the resulted perfect ${180}^{\circ }$ 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.

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• Magnetism
• Perovskites
• Ab initio molecular dynamics
• Density functional calculations