The electronic structure and spin polarization of Fe3-xMnxSi and Fe3-yMnSiy alloys.

First principle calculations using supercell approach and coherent potential approximation (CPA) are performed to investigate the electronic and magnetic structures of Fe_3-xMn_xSi and Fe_3-yMn_ySi_y alloys, where x, y=0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.5, 1.75, and 2.25. Using supercell calculations we obtained a metallic behavior for x=0, 0.25, and 0.5 in Fe_3-xMn_xSi alloys with spin polarizations of 24%, 39%, and 93%, respectively. The behavior starts to be half-metallic at x=0.75 with a small direct band gap that increases for higher concentrations of Mn. Among the half-metallic systems, only those of L21 structure at x=1 and 2 possess indirect band gaps along Γ-X symmetry line. The change of Si concentration in Fe_3-yMn_ySi_y structures retrieve the metallic behavior for all concentrations except y=1.25 that shows a half-metallic behavior with a direct band gap of 0.27 eV. We obtained a good agreement between supercell and CPA calculations for the values of the magnetic moment and the trends of the formation energies, which reveals the validity of the supercell approach in predicting the magnetic structure and the energetics of doped Heusler alloys. [ABSTRACT FROM AUTHOR]