Valence states of transition-metal ions and electronic structures of spinel [Fe.sub.1-x][Cu.sub.x][Cr.sub.2][S.sub.4]

The valence states and electronic structures of transition-metal ions in spinel [Fe.sub.1-x][Cu.sub.x] [Cr.sub.2] [S.sub.4] (0.1 [less than or equal to] x [less than or equal to] 0.5) have been investigated by using scanning photoelectron microscopy (SPEM), photoemission spectroscopy (PES), soft-X-ray absorption spectroscopy (XAS), and soft X-ray magnetic circular dichroism (XMCD). The experimental data have been compared to the calculated density of states (DOS). It is found that the valence states of Cr and Cu ions are nearly trivalent ([Cr.sup.3+]) and monovalent ([Cu.sup.+]), respectively. The Fe 2p XAS spectra of [Fe.sub.1-x][Cu.sub.2][Cr.sub.2] [S.sub.4] are very similar to that of Fe metal, indicating that Fe 3d states are strongly hybridized to S 3p states. The XMCD measurements for Fe, Cr, and Cu 2p states show evidence that the magnetic moments of Cr ions are antiparallel to those of Fe ions and that Cu ions are weakly polarized parallel to Fe ions. Valence-band PES reveals that Cr 3d states are located at ~ -1.5 eV, while Fe 3d states are very broad, in agreement with the calculated DOS. This study indicates that the minority-spin [e.sub.g] states of Fe 3d electrons are located very close to EF, suggesting that the hybridized Fe [e.sub.g]-S 3p states near EF play an important role in determining the transport properties of [Fe.sub.1]-x [Cu.sub.x[Cr.sub.2][S.sub.4] for x [less than oe equal to] 0.5. Index Terms--Fe[Cr.sub.2][S.sub.4], [Fe.sub.0.5][Cu.sub.0.5][Cr.sub.2] [S.sub.4], photoemission spectroscopy (PES), scanning photoelectron microscopy (SPEM), spinel, X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD).