Electronic structure of the full-Heusler Co $$_{2-x}$$ 2 - x Fe $$_{1+x}$$ 1 + x Si and half-Heusler CoFeSi alloys obtained by first-principles calculations and ultrasoft X-ray emission spectroscopy

We present a combined investigation of the electronic structure of bulk arc-melted full-Heusler Co $$_{2-x}$$ 2 - x Fe $$_{1+x}$$ 1 + x Si (x = 0, 0.5, 1) and CoFeSi alloys using density functional theory and ultrasoft X-ray emission spectroscopy. We perform first-principles calculations of the spin-polarized total and partial density of states for the Co and Fe 3d (s, p) as well as for the Si 3s (p, d) orbitals. It is demonstrated that only Co $$_{2}$$ 2 FeSi alloy exhibits a half-metallic behavior. However, the inverse CoFe $$_{2}$$ 2 Si alloy shows pseudogap and high spin polarization at the Fermi level. We carry out ultrasoft X-ray emission Si $$L_{2,3}$$ L 2 , 3 measurements, which provide the information about the local partial density of states of Si 3s and 3d orbitals in the valence band localized on Si atoms. We compare the measured spectra with our theoretical calculations and discuss them in terms of the contribution of s and d-electrons to the bonding. The Si and transition-metals sd and dd bonding formation is shown in the Co $$_{2-x}$$ 2 - x Fe $$_{1+x}$$ 1 + x Si and CoFeSi alloys. The high spin polarization values, along with the extremely high Curie temperature, make these compounds potential candidates for spintronic applications.