Effect of V substitution on structural, magnetic, transport and mechanical properties of the half-metal-type Heusler alloy Co₂FeGe

Half-metallic ferromagnets are ideal candidates for spintronic applications due to their ∼100% spin polarization. High Curie temperature T_c is one of the important prerequisite from the application point of view. Co₂Fe- based Heusler alloys in L2₁ structure have attracted great interest for this reason. We present a combined experimental and theoretical study of quaternary Heusler alloys Co_2-xV_xFeGe and Co₂Fe_1-xV_xGe (0 ≤ x ≤ 1) as promising candidates for spintronic applications. Single phase microstructures for arc-melted alloys are observed for V substitution for Co from x = 0.25 to x = 0.625, but when V substituites for Fe only x = 0.25 and 0.375 yield single phase microstructures. All single phase samples show fcc structures with L2₁ ordering, corroborated by X-ray diffraction. Low-temperature saturation magnetic moments agree well with our theoretical results and obey the Slater-Pauling rule, a prerequisite for half metallicity. All alloys are soft ferromagnets with high T_cs, allowing for applications at room temperature and above. Transport measurements are performed to elucidate the electronic structure of the alloys. Relatively high mechanical hardness values are also observed.