First-Principles Calculations Of Electronic And Spin Transport Properties Of Two-Dimensional Magnetic Half-Metallic Materials

The performance of conventional semiconductor integrated circuits is about to approach its limits and development is slowing down significantly.In order to solve the difficulties encountered in the development of electronics,spintronics came into being.Spintronics devices have the advantages of high integration,low energy consumption and fast computing speed compared to traditional electronic devices,breaking through the development bottleneck and greatly promoting the arrival of a new revolution in information technology.Since the discovery of graphene,two-dimensional（2D）materials have been extensively used in spintronics devices.However,many 2D materials have low spin polarisation rates and Curie temperatures,as well as no ferromagnetism,making them difficult to apply in practice.However,2D half-metals,Spin-gapless semiconductors（SGS）and bipolar magnetic semiconductors（BMS）are ideal for spintronics device applications due to their unique electronic and magnetic properties.The potential applications of two-dimensional multiferroic materials have also getting a lot of attention in nanoelectronic devices such as non-volatile memories and magnetic sensors.Therefore,the search for SGS and BMS and multiferroic materials with high spin polarisation rates and high Curie temperatures is of great importance for conducting spintronics research.In this paper,the electronic structure and magnetic properties of two-dimensional VSi₂X₄ and MnOX are investigated in depth by combining the First-principle and the non-equilibrium Green’s function to design two-dimensional transverse homogeneous junctions based on VSi₂P₄,and the corresponding results are given as follows:1.For the two-dimensional monolayer VSi₂X₄（X=N,P,As）,we performed molecular dynamics simulations and calculated its phonon spectrum,and found that the VSi₂X₄ monolayer is stable at room temperature.Calculations of its magnetic properties revealed that VSi₂X₄ is all intrinsically ferromagnetic.Calculations of their energy band structures indicate that VSi₂N₄ and VSi₂P₄ are type-Ⅱ SGS,and VSi₂As₄ is BMS.when stress is applied to all three,an electronic phase transition from type-Ⅱ SGS to metal to type-Ⅰ SGS occurs for VSi₂P₄,and from BMS to type-I SGS type to type-Ⅱ SGS occurs for VSi₂As₄.The Curie temperatures based on Monte Carlo simulations are calculated to be 230 K for VSi₂N₄,235 K for VSi₂P₄ and 250 K for VSi₂As_4.We also find excellent spin filtering and spin Seebeck effects in monolayers of VSi₂P₄.This work suggests that two-dimensional monolayers of VSi₂X₄（X=N,P,As）have great potential for spintronics applications.2.In two-dimensional MnOX（X=Cl,Br）,it is found by calculation that the monolayers of MnOX are all ferromagnetic half-metals and their properties are insensitive to stress.Based on the Monte Carlo simulations we predict Curie temperatures is 220 and 210 K for MnOCl and MnOBr,respectively,which can be regulated by the application of stresses.We have calculated the magnetic anisotropy energy（MAE）of MnOX and found that the MAE can be effectively modulated by external biaxial strain.We also demonstrate that the in-plane magnetic susceptibility axis of monolayer MnOBr can be reversed by external ferroelastic strain.Thus,the exploration of MnOX（X=Cl,Br）monolayers will provide new options for the application of 2D multiferroic materials.