Reasearch On The Electronic Structures And Magnetic Properties Of Some Quaternary Heusler Alloys With 4d Transition Metal Elements

In recent years,more and more quaternary Heusler alloys have reported to be half-metals.However,most of the reported Heusler alloys contain only 3d transition metal elements.It has been reported that the half-metallic band gap of Heusler alloy with 4d transition metal element is usually larger than that of the Heusler alloys with only 3d transition metal element^[76].In this dissertation,the electronic structures and magnetic properties of some quaternary Heusler alloys with 4d transition metal elements are calculated by first-principles calculations method.The main conclusions are as follows:(1)The electronic structures and magnetism of the quaternary Heusler alloys FeRuCrGe/Si have been studied.The results show that FeRuCrGe alloy is a zero-gap half-metal,and Fe Ru Cr Si alloy is a spin gapless semiconductor.They all exhibit ferrimagnetism.The total magnetic moments of them mainly originates from the 3d electrons of Cr atoms,while Ge/Si atom has almost no contribution.Near the Fermi level,the indirect band gap of Fe Ru Cr Si alloy mainly comes from the d electron hybridization between the nearest neighbor atoms:Fe and Cr.The ground state of these alloys can be maintained in a wide range under hydrostatic strain and tetragonal distortion.Furthermore,under the hydrostatic strain,FeRuCrGe undergos an interesting physical properties transition from half-metal--zero-gap half-metal--general ferrimagnetic metal,and Fe Ru Cr Si undergos a transition from metal--half-metal--spin gapless semiconductor--zero-gap half-metal--metal.Under the tetragonal distortion,FeRuCrGe alloy can translate between metal,zero-gap half-metal and metal,and Fe Ru Cr Si alloy can translate between metal,half-metal,spin gapless semiconductor,half-metal and metal.This interesting physical phenomenon indicates that these two quaternary Heusler alloys will be good potential candidates of new spintronic devices.(2)By replacing Ru element in FeRuCrGe/Si alloy with Rh/Pd element,we studied the electronic structure and magnetism of new quaternary Heusler alloys Fe YCr Ge/Si(Y=Rh/Pd).The results show that Fe Rh/Pd Cr Ge alloy are general ferrimagnetic metals,while Fe Rh/Pd Cr Si alloys are half-metals.It is found that Fe Rh/Pd Cr Si alloys show the same atomic and magnetic arrangements as Fe Ru Cr Si alloy,and their equilibrium lattice constant increases with the increase of the atomic number of Ru/Rh/Pd.For Fe Rh/Pd Cr Si alloys,the strong covalent hybridization between Fe atom and its nearest neighbor Cr atom leads to the wide half-metallic energy gaps around the Femi level.It can be found that Cr atom has a strong spin splitting for both Fe Rh Cr Si and Fe Pd Cr Si alloys.Thus,Cr atom is the main contributor to the total magnetic moment.Under hydrostatic strain,the half-metallicity of Fe Rh/Pd Cr Si alloy can be maintained in the wide range of-9.3%?0.5%and-4.4%?1%,respectively,implying that the half-metallicity of them is not sensitive to lattice compression.(3)The electronic structures and magnetism of Fe Ru Cr P and Fe Rh Cr P alloys with LiMgPdSb type structure have been studied.The calculatioional results show that Fe Ru Cr P is a ferrimagnetic half-metal and Fe Rh Cr P is a ferromagnetic half-metal,with large half-metallic band gaps of 0.39 e V and 0.38 e V,respectively.The total magnetic moments of Fe Ru Cr P and Fe Rh Cr P are 3?_B and 4?_B per formula unit,respectively,which follows the Slater-Paulig behavior of Heusler alloys:M_t=Z_t-24.Furthermore,the half-metallic properties of Fe Ru Cr P and Fe Rh Cr P compounds can be kept in a quite large range of hydrostatic strain(about-5.23%?1.39%and-9.31%?1.03%,respectively)and are quite robust against tetragonal deformation(c/a ratio in the range of 0.94–1.1and 0.97–1.1,respectively).Moreover,the large negative cohesion energy and formation energy of Fe Ru Cr P and Fe Rh Cr P compounds indicate that they can be synthesized experimentally.They are expected to become excellent providers of high spin polarization current for the future spin tronics devices.