Prediction of electronic structure and magnetic anisotropy of two-dimensional MSi2N4 (M=3d transition-metal) monolayers

Two-dimensional (2D) transition metal nitrides have potential applications in novel low-dimensional spintronic devices due to their unique properties such as higher surface area and electrical conductivity than graphene. Recently, the successfully synthesized MoSi2N4 monolayer has attracted much attention. In order to improve its application, MSi2N4 monolayers are systematically analyzed in this work, where M represents 3d transition metal. The electronic structure and magnetic anisotropy of MSi2N4 monolayers are calculated by first-principles calculations. It is found that ScSi2N4 and VSi2N4 monolayers are half-metallic. TiSi2N4 and CrSi2N4 monolayers are semiconductors. MnSi2N4, FeSi2N4, CoSi2N4, NiSi2N4, CuSi2N4 and ZnSi2N4 monolayers are metallic. By applying strain to MSi2N4, part of the metallic monolayers can be transformed into half-metallic or semi-conducting ones. The half-metallic VSi2N4 monolayer can be transformed into a metal or a semiconductor under biaxial strain. The magnetism of ZnSi2N4 disappears at compressive strain, while it transforms into a half-metallic at + 6 % tensile strain. Meanwhile, the magnetic anisotropy energy of ZnSi2N4 transformed from perpendicular magnetic anisotropy to in-plane magnetic anisotropy when tensile strains are applied. 2D materials with half -metallic abundance and perpendicular magnetic anisotropy have potential applications in spintronic devices.