Electronic Structures, Magnetism And Half-Metallicity Of Full-Heusler Alloys CR2YZ (Y=Mn,Fe,Co;Z=Al,Ga,Si,Ge,P,As):a First-Principles Study

In recent years, half-metallic materials have received growing attention due to their potential applications for spintronic devices. For the half-metallic materials, one of the spin-bands is partially filled, while there is a gap in the density of states for the other spin-band. Thus, one of the spin-bands is conductor, while the other is an insulator or semiconductor. The particular electronic structure leads to a complete spin polarization (P=100%) at the Fermi level.Among many half-metallic materials, Heusler alloys have attracted great attention because of the high Curie temperature and structural similarities with semiconductors. In this thesis, we use the full-potential linearized-augmented plane-wave (FLAPW) method as implemented in the FLEUR within the generalized gradient approximation (GGA) to study the electronic structure, magnetism and half-metallicity of full-Heusler alloys Cr2YZ (Y=Mn,Fe,Co; Z=Al,Ga,Si,Ge,P,As). The results are as follows:(1) The optimized lattice constants of Cr2MnZ (Z=Al,Ga,Si,Ge,P,As) are5.820A(Cr2MnAl),5.787A(Cr2MnGa),5.651A (Cr2MnSi),5.819A (Cr2MnGe),5.590A (Cr2MnP) and5.778A (Cr2MnAs) respectively; the density of states and band structures show that Cr2MnGa, Cr2MnSi and Cr2MnP are conventional ferromagnetic materials; Cr2MnAl, Cr2MnGe and Cr2MnAs are quasi half-metallic materials. With the uniform deformations, Cr2MnAl maintains its half-metallic nature in the range of the lattice constants from5.849to6.057A; Cr2MnGe and Cr2MnAs will lose their half-metallic nature. (2) The optimized lattice constants of Cr2FeZ (Z=Al,Ga,Si,Ge,P,As) are5.758A(Cr2FeAl),5.773A(Cr2FeGa),5.616A(Cr2FeSi),5.732A (Cr2FeGe),5.578A(Cr2FeP) and5.745A(Cr2FeAs) respectively; the density of states and band structures show that Cr2FeAl, Cr2FeGa, Cr2FeGe and Cr2FeP are conventional ferromagnetic materials; Cr2FeSi is paramagnetic material; Cr2FeAs is quasi half-metallic materials. With the uniform deformations, Cr2FeAs will lose its half-metallic nature.(3) The optimized lattice constants of Cr2CoZ (Z=Al,Ga, Si,Ge,P,As) are6.154A(Cr2CoAl),5.802A(Cr2CoGa),5.985A (Cr2CoSi),5.784A (Cr2CoGe),5.610A (Cr2CoP) and5.776A (Cr2CoAs) respectively; the density of states and band structures show that Cr2CoAl, Cr2CoGa, Cr2CoSi and Cr2CoGe are conventional ferromagnetic materials; Cr2CoAs is quasi half-metallic materials; Cr2CoP is a true half-metallic materials. With the uniform deformations, Cr2CoAs will lose its half-metallic nature; Cr2CoP can maintain its half-metallic nature in the range of the lattice constants from5.438to5.610A. Under the non-uniform deformations along the [001] direction, Cr2CoP will lose its half-metallic nature, regardless of the compression or elongation.