Photoemission satellites and electronic structure ofFe2O3

Abstract

The electronic structure of α-${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ with the high-spin $d^5$ ground-state configuration has been studied by ultraviolet photoemission spectroscopy with use of synchrotron radiation as well as by x-ray photoemission and Auger-electron spectroscopy. The results are interpreted in terms of the configuration-interaction theory based on a ${\mathrm{FeO}}_6$-cluster model. The main lines of the valence-band photoemission spectra are identified with Fe?d sup 5 ndash—ligand-hole final states produced by ligand-to-3d charge-transfer screening of 3d holes (3$d^4$ states), whereas the satellite at higher binding energies is assigned to unscreened (or poorly screened) 3$d^4$ final states. The Fe 3d versus O 2p partial density of states and symmetry characteristics of 3d-derived peaks are found to be quite different from assignments based on ligand-field theory or band theory. These results indicate that ${\mathrm{Fe}}_2$ ${\mathrm{O}}_3$ cannot be considered as a Mott-Hubbard insulator in its original sense but is classified as a charge-transfer-type insulator according to a theory of Zaanen, Sawatzky, and Allen. A possibility is suggested that the lowest unoccupied state is not Fe?d ndash—like but is the bottom of the Fe 4s band. The large exchange energy of the high-spin 3$d^5$ configuration is shown to greatly stabilize the localized 3d states relative to the itinerant state.