Study On Phase Transition,Magnetic Properties And Half Metallicity Properties Of Some V,Fe-Based Quaternary Heusler Alloys Based On First-Principles Calculations

The half-metallic Heusler alloy has the advantages of high magnetization,relatively easy synthesis,high Curie temperature,and complete electron conduction at the Fermi level,so it has a good application prospect in the field of spintronics.In this dissertation,OsTiVIn,Os Zr VIn,Ir Fe YSi(Y=Ti,Zr,Hf)and Rh Fe YSi(Y=Ti,Zr,Hf)of Li Mg Pd Sb structure are selected as research objects.On the basis of verifying their stability,mechanical stabilities,magnetic stabilities and half-metallic properties are investigated in detail.First,structural stabilities,half-metallic properties,magnetic properties and possible martensite phase transitions of Li Mg Pd Sn quaternary Heusler alloys OsTiVIn and Os Zr VIn were studied by using first-principles calculations based on density functional theory.There are three kinds of non-equivalent structures in the alloy.According to the ground state calculation results,it is found that the total energy of the two alloys is the lowest in the ferromagnetic state of the first type.The cell equilibrium lattice constants of OsTiVIn and Os Zr VIn are 6.372 and6.557?,respectively.The electronic band structure and density of states of the quaternary compounds at 0 GPa indicate that the spin-up electrons of OsTiVIn and Os Zr VIn are metallic electrons,but the spin-down electronic energy bands have half-metallic band gaps of 0.48 and0.78 e V,respectively,resulting in a stable half-metallic ferromagnetic behavior.The total magnetic moment of each proton cell is equal to 2μ_B with 100%spin polarizability near the Fermi energy level,and the magnetic moment is mainly provided by the 5d orbital of the Os atom and the 3d orbital of the V atom.The OsTiVIn alloy retains its half-metallic character at98 GPa,but beyond which it transitions to the metallic phase.No magnetic phase transition was found to occur over the entire pressure range.In addition,the half-metallic bandgap of Os Zr VIn is wider than most reported quaternary Heusler alloys and maintains half-metallic properties at100 GPa.Second,IrFeYSi(Y=Ti,Zr,Hf)and RhFeYSi(Y=Ti,Zr,Hf)were investigated,and their mechanical properties such as elastic constants,generation enthalpies,and phonon spectra were calculated at 0 GPa pressure to verify the structural stabilities.Also,the volume and energy curves show that it has the lowest energy in the first atomic occupation and the ferromagnetic state is energetically more favorable than the paramagnetic state.The energy band and density of states were also calculated,and the results show that Ir Fe YSi(Y=Ti,Zr,Hf)and Rh Fe YSi(Y=Ti,Zr,Hf)have metallic properties in the spin-up band and semiconducting and insulator properties in the spin-down band,with band gaps of 0.20,0.80,0.83,0.30,0.50,0.55 and 0.55 e V,respectively,at the equilibrium lattice constants.The contribution to the density of states is mainly from the 3d orbital of Fe atoms,as shown by the fractional wave density of states.The new quaternary Heusler half-metallic materials Ir Fe YSi(Y=Ti,Zr,Hf)and Rh Fe YSi(Y=Ti,Zr,Hf)proposed are mechanical,thermodynamical and dynamical stability,which increases the chance of successful experimental synthesis.This study may provide new material candidates for the fabrication of spintronic devices.