The Exploration And Studies On Physical Properties Of Several Highly-spin-polarized Materials With Heusler Structure

Heuser alloys contain rich physical phenomena. Previous investigations on Heuseralloys focused mainly on the alloys containing two transition metals of group7, group8and Cu. Many functional properties were found in these alloys. In this work, Heusler alloyscontaining two or three low-valence transition metals, especially Ti and V atoms, have beeninvestigated systematically in theory and experiment.Using first-principle calculations, the electronic structures, magnetic properties, origin ofthe band gap and the influence of spin-orbit coupling (SOC) on the electronic structureshave been studied for V2Re-based alloys. V2ReZ (Z=Al, Ga, In) alloys are predicted to behalf-metallic ferrimagnets at their equilibrium lattice parameters. V2ReB can be half metalwith the lattice distortion. The half-metallicity can be held in a quite wide lattice distortionfor the half-metallic V2Re-based alloys. The spin-orbit coupling increases the width of thehalf-metallic gap for the V2Re-based alloys.Ti2MnZ (Z=Al， Ga， In) alloys with cubic structure were synthesized. Usingfirst-principle calculations, we predicted that Ti2MnZ (Z=Al， Ga， In) alloys arecompletely-compensated ferrimagnetic semiconductor with a nearly spin-gaplesscharacteristic. Ti2MnZ (Z=Si，Ge，Sn，Sb，Bi) alloys show half-metallicity. These alloysfollow the Mt=Zt-18rule. The electronic structures, magnetism and origins of band gap ofTi2Cr-based alloys were studied. Ti2CrSn alloy is a completely-compensated ferrimagneticsemiconductor. By doping main-group congeners, the width of band gap can be adjustedcontinuously and achieve the real spin-gapless materials. By doping transition elements Fe,Co and Mn, we gain a series of half-metals. When substituting Sb and Bi for Sn, atransformation form semiconductor to half-metal occurs.A series of TiFeXY（X=Cr, Mn, Fe, Co, Ni;Y=Al, Ga,Si，Ge） quaternary alloys wereprepared. The effect of atomic radius and valence electron concentration on structure andphase component has been investigated. The quaternary alloys can form LMPS-typestructure, C14-type Laves structure and a hexagonal structure with189space group withthe different atomic radius and valence electron concentration. The magnetization curve ofTiFeNiGa and TiFeNiAl alloys perform a wasp-waist shape. There are two magnetictransition points for TiFeMnGa alloy and we predict that it is a good candidate formagnetostrictive materials.We studied the effect of doping Fe, Co and Cr elements on properties of NiMnSb alloy.The Fe and Co elements can occupy the empty sites in NiMnSb alloy and then form thequaternary full-Heusler alloy (Ni-Mn-Fe-Sb/Ni-Mn-Co-Sb) with the atomic ratio is close to1:1:1:1. However, Cr element can hardly be dissolved in NiMnSb alloy. When the interfacewas MnSb-Cr, the superlattice which consists with NiMnSb alloy and Cr has a largespin-polarized ratio at the Fermi level.