Influence of Cr-substitution on the structural, magnetic, electron transport, and mechanical properties of Fe3−x Cr x Ge Heusler alloys

We performed combined experimental and theoretical studies of the effect of Cr substitution for Fe on the structural, magnetic, transport, electronic, and mechanical properties of Fe${}_{3-x}$Cr${}_x$Ge ($0⩽x⩽1$) intermetallic alloys. Single phase microstructures are observed for $x⩽0.70$. Higher Cr concentrations $x>0.70$ are multi-phased. A hexagonal D0${}_{19}$ structure is found for all Cr concentrations, with the lattice parameters increasing systematically with an increasing Cr content. All the alloys in the series are found to be ferromagnets with large magnetization values of about 6 ${\mu }_B/f.u$. and high Curie temperature above room temperature. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule. The density functional theory calculation reveals that Cr substitution energetically favours one of the Fe sites in Fe₃Ge. The electrical resistivity measured over the temperature range from 5 K to 400 K shows metallic behavior, with a residual resistivity ratio that decreases with Cr content. Vicker's hardness values are observed to increase with increasing Cr content to approximately 5 GPa.