First-principles Study Of Mn-based Heusler Alloy In Spintronics

Spintronics device has attracted the research interest of many researchers owing to its special transmission properties.The representative half-metallic materials have also developed rapidly.The half-metallic material has a special band structure,one side passes through the Fermi level to reflect the metallicity;another side has a bandgap and exhibits semiconductor properties.This results in half-metallic materials with 100%spin polarization at the Fermi level,which greatly increases the electron transfer rate.This paper used First-principles calculations to study the structure stability and phase transition,electronic properties,magnetic properties,mechanical properties and occupancy of binary,ternary,and quaternary Mn-based Heusler alloys Mn₃Ga,Mn₂YGa?Y=V,Nb,Ta?,ScMnVGa?type?,?,??.Firstly,the structure of the Mn-based Heusler alloy was optimized,and the E-V curves of Mn₃Ga,Mn₂YGa?Y=V,Nb,Ta?,ScMnVGa?type?,?,??were calculated and fitted to the Birch-Murnaghan equation.We obtained the equilibrium lattice constants a???and bulk modulus B₀ of each structure.Comparing these results with other theoretical calculations and experimental results,it is found that they are in good agreement.Since the shape memory effect of Heusler alloy is a phase transformation process from the cubic austenite phase to the tetragonal martensite phase,we calculated the tetragonal deformation of several compounds and found that Mn₃Ga,Mn₂YGa?Y=V,Nb,Ta?have one or two tetragonal martensite phases beside the cubic phase.Thermodynamic and mechanical stability calculations were performed on the structures of these cubic and tetragonal phases.As a result,it was found that the cohesive and formation energies of all compounds are less than zero,which meets the thermodynamic stability.Mn₃Ga?cubic?and Mn₂TaGa?tetragonal?do not meet the mechanical stability.The electronic and magnetic properties of Mn-based Heusler alloy are also studied in detail.The band structure results show that Mn₂VGa?cubic?,Mn₂NbGa?cubic?,Mn₂NbGa?c/a=0.96?and ScMnVGa type-?,?are half-metallic.For Mn₂VGa and Mn₂NbGa,the half-metal properties maintain certain stability during the change of lattice constant and tetragonal deformation.The density of state shows that the half-metallic properties of these compounds mainly originate from the d orbital hybrid of Mn atoms and other transition atoms?V,Nb,Ta?.The magnetic results showed that ScMnVGa type-?,?showed antiferromagnetism,while Mn₃Ga?tetragonal?,Mn₂VGa,Mn₂NbGa,and Mn₂TaGa?cubic?were all ferrimagnetic.The magnetic moments of several compounds with half-metallic properties are integers and satisfy the Slater-Pauling rule.The mechanical properties of Mn-based Heusler alloy were studied by VRH approximation,including bulk modulus B,shear modulus G,Young's modulus E,Poisson's ratio?,B/G value,and anisotropy.It was found that the cubic structure of ScMnVGa type-?is between brittleness and ductility;ScMnVGa type-?shows brittleness;Mn₂VGa,Mn₂NbGa and Mn₂TaGa are all greater than 1.75 and show ductility.In the tetragonal structure,Mn₃Ga has ductility,and the tetragonal structure of Mn₂VGa shows brittleness;Mn₂NbGa has two tetragonal structures,c/a=1.94 means that the material is brittle,and c/a=1.16 shows ductility.Anisotropic results indicate that all compounds are anisotropic materials.Since the properties of the quaternary Heusler alloy are greatly affected by atomic arrangement,the effects of the atomic disorder of ScMnVGa on the electronic structure and spin polarizability are studied in this paper.Constructed 12 kinds of antisite and 6kinds of swap disorder,type-?has 3 kinds of antisite disorder and 1 kind of swap disorder,type-?has 6 kinds of antisite disorder and 1 kind of swap disorder,and their spin polarizability is still 100%.It is clearly found that the ability of type-?to resist disorder is stronger than that of type-?and that both structures are more resistant to antisite disorder than swap disorder.