First-principle Calculations On Two-dimensional Square Magnetic Half-metals

Spintronics processed informations by using the spin degrees of freedom of electrons,it has gained widespread attention in the fields of quantum computing and information storage due to high operating speed and low power consumption.Two-dimensional（2D）intrinsic ferromagnetic（FM）half-metals with high spin polarization rates have a great promise for high performance magnetic memory and spintronic devices.The magnetic materials with high Curie temperature（T_C）could work effectively in applications.At present,most 2D intrinsic magnetic materials have the disadvantage of low T_C or unstable properties,which is greatly limited in practical applications.Finding stable 2D intrinsic ferromagnetic materials with high T_C is an important direction in the field of 2D magnetism.In this paper,we have predicted the magnetic and electronic properties of the 2D intrinsic ferromagnetic half-metallic Cr Br₂and MNBr（M=Mo,Cr,V）by first-principles calculations.In addition,we have also performed strain and carrier doping to modulate the physical properties of the materials.Firstly,we have predicted the stability,electronic and magnetic properties of the mono-layer square Cr Br₂by using the first-principle.Monolayer Cr Br₂is an intrinsically FM half-metallic material with a wide half-metallic band gap.Monte Carlo simulations based on the Heisenberg model predicted the T_C of 212 K.In addition,strain have been applied to mono-layers Cr Br₂,application of a uniaxial compressive strain of 2.7%or a biaxial compressive strain of 2.1%caused the ferromagnetic-antiferromagnetic phase transition,the biaxial ten-sile strain larger than 9.3%results in the electronic performance transition from half-metal into semiconductor.The results shown that monolayer square Cr Br₂is intrinsic half-metallic material with high T_C and controlled magnetism,it has a widespread applications in spin-tronic.Secondly,we have performed systematic calculations of monolayer MNBr（M=Mo,Cr,V）by first-principles calculations,including stability,electronic and magnetic properties.Monolayers of MNBr（M=Mo,Cr,V）are predicted to be intrinsically FM half-metallic ma-terials with a spin polarizability of 100%and a wide half-metallic band gap.By using Monte Carlo simulation with Heisenberg model,estimated the T_C of Mo NBr,Cr NBr and VNBr as402 K,673 K and 120 K.The magnetic anisotropy energy（MAE）of monolayer Mo NBr,Cr NBr and VNBr are 487.64μe V/Mo,420.18μe V/Cr and 698.84μe V/V,respectively.In addition,the projected magnetic moments of the metal atoms and the T_C of the system could modulate significantly by strain.Taking Mo NBr as an example,we have investigated the effects of uniaxial strain and carrier doping on the projected magnetic moments of Mo atoms and the T_C of the system,and have analysed the causes of the FM-AFM magnetic phase transition due to carrier doping.