First-principles Study Of The Full Heusler Alloy Ti 2 FeSn And Its (100) Surface

With the development of the spintronics,half-metallic materials have become the center of scientific research.Half-metallic materials have 100%spin-polarization,this properties indicate half-metallic materials have extensive application prospects when used in the magnetic tunnel junctions(MTJs).Among many half-metallic materials,Heusler alloys have high Curie temperature and their structures are compatible with the conventional semiconductors,these properties are very beneficial to spin transport at room temperature.In the MTJs,the phenomenon of spin transport is the prerequisite for many applications,thus Heusler alloys attract many attentions.In this paper,using the Vienna ab-initio simulation package(VASP),based on the first-principles calculations,we systematic analyze full-Heusler alloy Ti2FeSn.By structural analysis,we regard Ti2FeSn as a kind of Hg2CuTi-type full-Heusler alloy,namely inverse Heusler alloy.In this kind of structure,two Ti atoms are located in the 4a(0,0,0)and 4b(0.25,0.25,0.25)Wyckoff coordinates sites,Fe atom occupies 4c(0.5,0.5,0.5)Wyckoff coordinates sites,Sn atom occupies 4d(0.75,0.75,0.75)Wyckoff coordinates sites[14].Considering in the MTJs,the Ti2FeSn thin films should be used.So we also investigate five different terminations of the(100)-oriented thin films of the Ti2FeSn.We list our received valuable results as follows:1.For the Ti2FeSn Heusler alloy,the structure is the Hg2CuTi-type because the valance electrons for the Ti atom are less than those of the Fe atom.The equilibrium lattice constant is 6.326A,for the spin-down sub-band,the band gap is 0.68eV.the band gap can be attributed to the splitting:t2g-ti..The magnetic moment for the per formula unit is 2?B,and satisfies the Slater-Pauling rule.2.By natural cleaving,we can acquire the TiFe and TiSn terminations of the(100)-oriented thin films of the Ti2FeSn,we also create three artificial terminations:FeFe*,TiTi*and SnSn*terminations by substituting Ti with Fe on the TiFe surface,Fe with Ti on the TiFe surface and Ti with Sn on the TiSn surface.The TiSn termination is the most stable one while the SnSn*termination is the most unstable one.Only the TiFe and TiSn terminations can preserve the half-metallicity,the band gap for the TiFe termination is only 0.08eV and the half-metallicity for this termination is very unstable,but the band gap for the TiSn termination is 0.36eV and the half-metallicity is stable,combined with its lowest surface energy,the TiSn termination is very suitable to be used in the MTJs.The spin polarizaitons for the FeFe*,TiTi*and SnSn*terminations are 74.9%,72.8%and 72.1%,respectively,the half-metallicity for these terminations is destroyed because of the surface states,the atomic magnetic moments for the surface layers and subsurface layers for these terminations are very different from those in the bulk system.