Impact of excess iron on the calculated electronic and magnetic properties of Co3−xFexSi Heusler-compound

Ab initio density functional calculations are performed on the Co3−xFexSi alloys with variable iron composition (1 ≤ x ≤ 3). The evolution of the structural, electronic, and magnetic properties is investigated within different levels of approximations. These alloys crystallize in cubic Heusler structures, which evolve from the regular L21 structure for Co2FeSi to the inverse X structure for x ≥ 2. Using on-site Coulomb interactions of Ueff(Co) = 3.07 eV and Ueff(Fe) = 3.4 eV is found to describe consistently the experimental properties for x ≤ 2. A good agreement between calculated and experimental magnetic moments is found for the cubic inverse Heusler phases without the addition of Hubbard-model. The spin polarization is found to range from 1 for Fe concentrations of x ≤ 2, indicating the half-metallic character, to −0.29 at x = 3.