Resonant photoemission study of pyrite-type NiS2, CoS2 and FeS2

The electronic structure of pyrite-type ${\mathrm{NiS}}_{2}$, ${\mathrm{CoS}}_{2}$, and ${\mathrm{FeS}}_{2}$ has been studied by photoemission spectroscopy. From resonant photoemission studies and configuration-interaction cluster-model analysis of the spectra, ${\mathrm{NiS}}_{2}$ is found to be a charge-transfer-type insulator, the band gap of which is formed between the occupied S 3p and the empty Ni 3d states. Cluster-model calculations indicate that the short Fe-S distance favors the low-spin (S=0) ground state in ${\mathrm{FeS}}_{2}$ compared to the high-spin FeS. Resonant photoemission results indicate a sign of electron correlation in the nonmagnetic semiconductor ${\mathrm{FeS}}_{2}$. \textcopyright{} 1996 The American Physical Society.