A study of the FeX (X=Si, Ge) system electronic structure by X-ray photoelectron spectroscopy

For the two stoichiometric compounds FeSi and FeGe, the X-ray photoelectron spectra of valence bands are obtained and the calculations of their electronic structure are carried out by the first principles full-potential linear muffin-tin-orbital method. For FeSi, which is nonmagnetic, a good agreement of the calculated density of states and the X-ray photoelectron spectrum (AlKα excitation) is obtained in both the peak positions and the width of energy gap. For FeGe, which is antiferromagnetic, neither the nonspin-polarized nor the antiferromagnetic calculations shows good agreement with the experiment, and the former clearly suggests instability of the paramagnetic state. In both compounds the calculation reveals a remarkable degree of p–d-hybridization and covalency, which are evaluated quantitatively. In FeGe a paradoxical result is obtained, that the covalency of the FeFe bond is higher than the covalency of the bond FeGe.