Theoretical Study On Electronic Structure And Magnetic Properties Of Alloy Compound Ti_xCr_1-xSi₂N₄ Monolayer

The spintronic devices,which rely on the spin of electrons to process,store and transmit data,are expected to break the performance limits of traditional electronic devices.Two-dimensional（2D）magnetic half-metals with 100%carrier polarizability are promising to facilitate the miniaturization and integration of spintronic device units.This kind of magnetic system enables the efficient generation and injection of spin polarization currents and is regarded as an ideal candidate for high-performance spintronic devices.However,the long range magnetic order is easily destroyed by thermal motion in 2D magnetic materials,and the magnetic half-metallic systems are relatively insufficient,which means that the exploration for high temperature 2D magnetic half-metals are of practical significance to promote the design of spintronic devices.Modifying the electronic structure of magnetic semiconductors by transition metal alloying is one of the effective methods to construct the inherent half-metallicity in 2D magnets.Recently,a new family ofMo Si₂ N₄-type monolayer was synthesized by chemical vapor deposition method.This 2D system exhibits the excellent environmental stability with a crystal structure consisted of septuple atomic layers and no corresponding bulk phase structure.Although the robust half-metallic system does not exist inMA₂ Z₄（M is transition metal element,A and Z areIV_A and _AV group element,respectively）monolayer,the half-metallicity is still expected to be added to several magnetic semiconductors with lattice dynamic stability by alloy engineering.Based on antiferromagnetic semiconductorCr Si₂ N₄ monolayer,we predict a ferromagnetic half-metallicity（FHM）in alloy compoundTi₀.₅C r_0.5S i₂ N₄ monolayer with a minority-spin gap of 3 e V and a considerable magnetic anisotropy energy by applying the first-principles calculation.The FHM ofTi₀.₅C r_0.5S i₂ N₄ are robust against biaxial strain from-3%to 3%.TheTi₀.₅C r_0.5S i₂ N₄ belongs to XY ferromagnet with negligible in-plane magnetocrystalline anisotropy and the Curie temperature is estimated to be near room temperature by Monte Carlo simulation with the consideration of symmetric and antisymmetric exchange interactions as well as single ion magnetocrystalline anisotropy term.Such a FHM at room temperature may be permitted in the range of Ti concentrations from 0.5 to 0.75.Strong d–d hybridization between Cr and Ti atoms and the larger exchange splitting of Cr-orbitals with respect to Ti-orbitals are origin of the HM and magnetic moment of Cr atom,and ferromagnetic coupling between Cr atoms is due to the Cr–N–Cr superexchange interaction.Besides,the applied potentials ofTi₀.₅C r_0.5S i₂ N₄ are further expanded by the large Young’s modulus and strong bending resistance.Thus,the rich Ti-alloyedCr Si₂ N₄ monolayers are noteworthy candidates for generating spin current source.