Structural, electronic, magnetic, transport and mechanical properties of the half-metal-type quaternary Heusler alloy Co2Fe1-xVxGe

Abstract

Abstract We report on the bulk properties of the Heusler alloy system Co 2 Fe 1 - x V x Ge 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 ( ∼ 800 K). Magnetization measurement shows the saturation magnetization to be 5.21 μ B / f . u . and 4.78 μ B / f . u . for Co 2 Fe 0.75 V 0.25 Ge and Co 2 Fe 0.625 V 0.375 Ge 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 Co 2 FeGe. Relatively high mechanical hardness values are also observed.