A good field to develop new materials with half metallicity is the quaternary Heusler alloys. The preferred route is to combine the compounds that have been already grown in Heusler structure. As a typical example, the quaternary LiMgPdSb-type CoFeMnSi have been investigated in detail. For the quaternary LiMgPdSb-type compounds, three nonequivalent structures exist. From the calculated density of state (DOS) results, it can be seen that one superstructure shows half metallicity. The second superstructure has a pseudogap at the Fermi level. The third superstructure shows metallic behavior. Based on the analysis of the measured XRD pattern and magnetization curve, we can deduce that the CoFeMnSi compound is crystallized in the structure where half metallicity occurs. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3062812

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A series of Fe2YSi (Y = Cr, Mn, Fe, Co, Ni) alloys were synthesized and their electronic and magnetic properties were studied both theoretically and experimentally. In particular, a novel Heusler alloy Fe2CrSi single phase was synthesized by means of the melt-spinning method. First principles FLAPW calculations were performed on Fe2YSi alloys. Based on the results, Fe2CrSi is predicted to be a half-metallic ferromagnet with a spin moment of 2μB/f.u. and a gap of 0.42 eV. Fe2MnSi is also half-metallic in the ferromagnetic state. The saturation magnetic moments at 5 K for this series of alloys fit the theoretical calculations well. Specifically, the saturation magnetic moment of Fe2CrSi is 2.05μB/cell, which agrees with the ideal value of 2μB derived from the Slater–Pauling rule. The Curie temperatures of Fe2YSi alloys are all higher than 500 K except for Fe2MnSi, which has a TC below room temperature. Finally, the effect of lattice distortion on the electronic and magnetic properties of Fe2CrSi and Fe2CoSi was studied. It is found that Fe2CrSi is half-metallic from −3% to +1% uniform lattice distortion, and this character is preferred in systems containing large strain, such as melt-spun ribbons or thin films.

The Co2NiGa alloy with a fcc structure was synthesized by different methods, arc-melting and mechanical alloying. In contrast with the solid solution state in melted Co2NiGa, an intermetallic structure, highly ordered atomic arrangement has been verified in ball-milled sample by x-ray diffraction examination and Rietveld analysis. This ordered structure increases the saturation magnetization about 40% higher than that of solid solution sample. A highly ordered Co2NiGa intermetallic compound model was established for carrying out first-principles calculation. The obtained electronic structure and the molecular moment are quite consistent with the experimental results. The characterization of the samples prepared in different alloying processes is also reported.