Effect of mixing the low-valence transition metal atoms Y = Co, Fe, Mn, Cr, V, Ti, or Sc on the properties of quaternary Heusler compounds Co2−xYxFeSi (0≤x≤1)

In this paper we report an experimental study of structural, magnetic, and mechanical properties of quaternary Heusler alloys ${\mathrm{Co}}_{2\ensuremath{-}x}{Y}_{x}\mathrm{FeSi}$ ($Y$ = Co, Fe, Mn, Cr, V, Ti, or Sc, $0\ensuremath{\le}x\ensuremath{\le}1$) and the experimental findings are supported by ab initio electronic structure calculations. The alloys were synthesized using an arc-melting technique. Single phase microstructures are observed for all alloys substituted with low-valence transition metals $Y$ except Sc. X-ray powder diffraction patterns at room temperature show the presence of Heusler-like face-centered cubic crystal structure in all single phase specimens. The low-temperature saturation magnetic moments, as determined from magnetization measurements, agree fairly well with our theoretical results and also follow the Slater-Pauling rule of thumb for half-metals, a prerequisite for half-metallicity. The alloys are predicted to exhibit half-metallic ferromagnetism by ab initio electronic structure calculations using the $\mathrm{GGA}+U$ approach. All stable compounds are observed to have high Curie temperatures with linear dependence with the valence electrons concentration in the alloys. Relatively high hardness values are also measured, approaching 15.7 GPa for Ti-substituted material, highest among the values reported for Heuslers so far. All these properties strongly suggest the alloys are promising for the spintronic applications at room temperature and above.