Electronic structure of 3d transition metal pyrites MS₂ (M = Fe, Co or Ni) by analysis of the M 2p core-level photoemission spectra

We have reinterpreted the metal 2p core-level x-ray photoemission spectra of the 3d transition-metal pyrites FeS₂, CoS₂ and NiS₂ using a new version of the single-impurity cluster model which includes the effects of charge transfer to the conduction band. By accounting for the effective screening of the strong core-hole potential involving the unfilled S 3p σ* orbitals on the ligand sites, we can successfully model the highly asymmetric lineshapes and weak satellite structures found for FeS₂ and CoS₂. Reduced screening in NiS₂ leads to the appearance of strong satellite structures and the spectrum is best interpreted using the screening channel to the narrow upper Hubbard band. These results indicate the importance of the empty ligand orbitals when interpreting the physical properties of the pyrite-type chalcogenides.