Electronic structures and magnetic moments of Fe_3+ySi_1-y and Fe_3-xV_xSi alloys with DO₃-derived structure

We present ab initio calculations of magnetic moments and local electronic densities of states in binary Fe_3+ySi_1-y and ternary Fe_3-xV_xSi random alloys with DO₃-derived structures. The local-spin-density approximation, the linear muffin-tin orbital method, and the coherent-potential approximation (LMTO-CPA) were used. In Fe_3+ySi_1-y the excess (as compared to Fe₃Si) Fe atoms occupy the Si[D] sites of the Fe₃Si host and create a strong d scattering. A realistic-alloy calculation thus requires the application of the CPA. In both types of alloys the moments of Fe atoms occupying the B sites remain essentially unchanged when the concentrations (y in Fe_3+ySi_1-y, x in Fe_3-xV_xSi) are varied. The Fe[A,C] moments vary almost linearly with y and x, in agreement with experimental observations. The sublattice density-of-states functions provide insight into the site preference for substitutional transition-metal impurities in Fe₃Si.