Influence of atomic substitution on the structural stability and half-metallicity of Fe2-xCrxCoSi (x=0 to 1) alloys

Bulk Fe2-xCrxCoSi (x = 0, 0.25, 0.5, 0.75, and 1) Heusler alloys have been prepared by arc melting method. Alloys with 0 <= x <= 0.75 show a highly ordered phase pure XA structure. However, 17 % of an impurity (A15 phase) was detected in the alloy with x = 1. The saturation magnetization (M-s) and Curie temperature (T-C) decreased linearly with an increase in Cr content for alloys with x <= 0.75. M-s measured at 5 K followed the Slater-Pauling rule for half-metals. Ab initio calculations with the GGA + U approach revealed that spin polarization (P) increased with an increase in Cr and eventually reached 100 % for the alloys with x = 0.5. Though Fe-Co disorder affects P, it is still high (>98 %) for alloys with x >= 0.5. Despite the smaller bandgap (0.61 eV) of Fe1.5Cr0.5CoSi than FeCrCoSi (0.91 eV), it has higher M-s, elevated T-C, and 100 % P. These factors, coupled with the challenges associated with obtaining phase pure FeCrCoSi alloy, make Fe1.5Cr0.5CoSi a preferred candidate for spintronic device applications.