Spin-valley coupling in a two-dimensional V Si2N4 monolayer

Materials that integrate magnetism, miniaturization, and valley properties hold potential for spintronic and valleytronic nanodevices. Recently, ferromagnetism was reported to be able to exist in the V Si₂N₄ monolayer which is half-metallic and belongs to a new kind of two-dimensional material [Hong et al., Science 369, 670 (2020), 10.1126/science.abb7023]. Using first-principles calculations and model analysis, we find that V Si₂N₄ is a ferromagnetic semiconductor harboring valley-contrasting physics and a magnetic critical temperature over room temperature. By tuning magnetization orientation from in plane to out of plane, valley polarization can be generated, resulting in the anomalous valley Hall effect in V Si₂N₄ . Furthermore, we obtain the formula for energy splitting of valleys and adopt a tight-binding model for V Si₂N₄ , which elucidates the physical mechanism of spin-valley coupling. More interestingly, under 4% tensile strain, the intrinsic magnetic anisotropy of V Si₂N₄ becomes out of plane, and spontaneous valley polarization is achieved. Our results highlight that V Si₂N₄ is a good candidate for spintronic and valleytronic applications.