Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi

We report a combined theoretical and experimental investigation of half-metallic ferromagnetism in equiatomic quaternary Heusler alloy CoRuMnSi. Room temperature XRD analysis reveals that the alloy crystallizes in L2(1) disordered structure instead of pristine Y-type structure due to 50% swap disorder between the tetrahedral sites, i.e., Co and Ru atoms. Magnetization measurements reveal a net magnetization of nearly 4 mu(B) with Curie temperature, T(C )of similar to 780 K. Resistivity measurement reveals the presence of localization effect below 35 K while above 100 K, a linear dependence is observed. The majority spin band near the Fermi level clearly indicates the overlap of flat e(g) bands with sharply varying conduction bands that are responsible for the localization. In-depth analysis of the projected atomic d-orbital character of band structure reveals unusual bonding, giving rise to the flat e(g) bands purely arising out of Ru ions. Co-Ru swap disorder calculations indicate the robustness of half-metallic nature, even when the structure changes from Y-type to L2(1)-type, with no major change in the net magnetization of the system. Thus, high T-C robust stability, and half-metallic nature make this alloy a promising candidate for further exploration from the point of view of applied spintronics.