Structural, electronic, magnetic, transport and mechanical properties of the half-metal-type quaternary Heusler alloy [formula omitted][formula omitted][formula omitted]Ge

Abstract

We report on the bulk properties of the Heusler alloy system Co2Fe1-xVxGe with 0⩽x⩽1 in steps of 0.125. We find single-phase alloys only for x=0.25 and x=0.375, both of which exhibit an L21 crystal structure. The alloys are found to be soft ferromagnets with high Curie temperatures (∼800K). Magnetization measurement shows the saturation magnetization to be 5.21 μB/f.u. and 4.78 μB/f.u. for Co2Fe0.75V0.25Ge and Co2Fe0.625V0.375Ge respectively, in good agreement with the values expected from a Slater-Pauling rule for half metals. In zero applied magnetic field, the resistivity versus temperature of these alloys does not display the usual T2 dependence at low temperatures indicative of electron-magnon scattering, another indirect suggestion of half metallicity. Our ab initio calculations also predict half-metallic character in the alloys after V substitution. The large exchange splitting between the occupied majority- and unoccupied minority-spin states leads to the Fermi level almost intersecting a peak in the V majority density of states. This leads to a markedly higher spin polarization upon V doping, making V an ideal dopant for achieving half-metallic behavior in Co2FeGe. Relatively high mechanical hardness values are also observed.