Interplay Between Mn, Fe, and Co in the Co2FeGe Alloy to Design Novel Singe-Phase Compounds with Potential Spintronic Application

Abstract

While the half-metallic Heusler alloys are considered ideal materials to be used in magnetic tunnel junctions, spin-filters, and spin valves, the search for new candidate half-metal remains an active field of research [1]. One of the ways of rational material design is by doping, which is useful not only to tailor the electric and magnetic properties but also to stabilize a single-phase compound [2, 3]. In this work, we show how the introduction of Mn helps to stabilize a single-phase compound and to tune half-metallic character in the Co2FeGe alloy, which otherwise is a multi-phased normal ferromagnet. We have investigated three substitutional series viz; (Co2-αMnα)FeGe, (Co2-αFeα)MnGe, Co2(FeαMn1-α)Ge, that can be generated from the intermixing of Mn, Fe, and Co by keeping the Ge content constant in the Co2FeGe alloy. These series cover all possible site doping that can be made for a magnetic atom in a full Heusler alloy and allow us to directly compare their magnetic and electric properties. First principles calculations performed using the generalized gradient approximation (GGA) predict that a half-metal is obtained in Co2(FeαMn1-α)Ge series while the other two series generate “near half-metallic” alloys. The experimental investigation of bulk samples of the (Co2-αMnα)FeGe series shows that a single-phase compound can be achieved up to α = 1.25. For all the single-phase compounds, the magnetic moment agrees reasonably well with the Slater-Pauling moment and a very high Curie temperature (~ 1000 K) is measured for low α. The experimental investigation of other series is currently underway; however, the preliminary results show that these series also generate single-phase compounds. Hence by doping Mn, Fe, and Co for one another, many single-phase compounds can be designed from Co2FeGe, with potential half-metallic behavior that can have actual use in spintronic devices