First-principles Study On The Electronic Structures And Magnetic Properties Of Two-dimensional Metal Nitrides

With the increasing miniaturization of components in integrated circuits,the development of nano spintronic materials has become a new research hotspot.Two-dimensional metal nitrides have become one of the excellent candidate materials in the field of spintronics because of their high structural stability,excellent electronic and mechanical properties,and so on.There are various types of two-dimensional metal nitrides,and some transition metal nitrides exhibit intrinsic magnetism because of unpaired electrons.In addition,although group ⅢA and group ⅢB nitrides are non-magnetic semiconductors,they are expected to be magnetized by methods such as doping atoms.In this paper,two-dimensional h-InN,t-AlN,t-ScN and so-MnN monolayers are used as the research objects.The electronic structures and magnetic properties of two-dimensional atom-doped h-InN,t-AlN and t-ScN and intrinsic so-MnN materials are investigated by using first-principles method.Meanwhile,biaxial strain is applied to regulate their physical properties.The main results are as follows:(1)In the study of h-InN monolayer doped with transition metal atoms Cr,Fe and Ni.It is found that the Cr and Fe doped h-InN monolayers are both magnetic semiconductors,while the Ni doped h-InN monolayer is a half-metal.The Cr-doped h-InN monolayer can exhibit room temperature ferromagnetism.The Fe and Ni doped h-InN monolayers have antiferromagnetic and ferromagnetic characteristics,respectively.Under the biaxial tensile strain,the h-InN monolayers doped with Cr,Fe and Ni can occur semiconductor-metal transition.(2)Both Be and C-doped t-AlN monolayers are magnetic semiconductors,and have the d~0 ferromagnetic characteristics.Mediated by the dispersed spin density,the Be and C-doped t-AlN monolayers exhibit long-range ferromagnetic coupling characteristics.Biaxial strain can modulate the band gaps of doped systems.The Be-doped t-AlN monolayer transformes into half-metal under a biaxial compressive strain of-4%.(3)After doping V,Cr,Mn and Fe in the t-ScN monolayer,it is found that all of these doped systems are magnetic.The change of the distance between two doped atoms can transform the magnetic coupling characteristics of these doped systems.The biaxial tensile strain does not change the semiconductor characteristic and magnetic moment of the doped systems.But under larger biaxial compressive strain(-6%),the V-doped t-ScN monolayer transforms into a magnetic metal.Under the biaxial compression strains of-4%and-6%,the Fe-doped t-ScN monolayer occurs transition from a low-spin state to a high-spin state.(4)The so-MnN monolayer is constructed by periodic arrangement of four-and eight-membered rings.The study shows that the so-MnN monolayer is energetically,dynamically,thermally and mechanically stable,and exhibits the intrinsic ferromagnetism and half-metallicity.The spin-up band crosses the Fermi level,while the spin-down band has the characteristic of direct band gap semiconductor.The Curie temperature T_C of so-MnN monolayer increases gradually under the biaxial strains from 0 to 3%,while the T_C has a decreasing trend under the biaxial strains from 0 to-3%,and the biaxial strain does not change its ferromagnetic and half-metal properties.