Electronic structures and magnetic moments of ${\mathrm{Fe}}_{3+\mathit{y}}$${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$ and ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$${\mathrm{V}}_{\mathit{x}}$Si alloys with ${\mathit{DO}}_3$-derived structure

We present ab initio calculations of magnetic moments and local electronic densities of states in binary ${\mathrm{Fe}}_{3+\mathit{y}}$ ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$ and ternary ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$ ${\mathrm{V}}_{\mathit{x}}$Si random alloys with ${\mathit{DO}}_3$-derived structures. The local-spin-density approximation, the linear muffin-tin orbital method, and the coherent-potential approximation (LMTO-CPA) were used. In ${\mathrm{Fe}}_{3+\mathit{y}}$ ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$ the excess (as compared to ${\mathrm{Fe}}_3$Si) Fe atoms occupy the Si[D] sites of the ${\mathrm{Fe}}_3$Si 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 ${\mathrm{Fe}}_{3+\mathit{y}}$ ${\mathrm{Si}}_{1\mathrm{-}\mathit{y}}$, x in ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$ ${\mathrm{V}}_{\mathit{x}}$Si) 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 ${\mathrm{Fe}}_3$Si.