Valence States of Transition-Metal Ions and Electronic Structures of Spinel Fe1−xCuxCr 2S4

The valence states and electronic structures of transition-metal ions in spinel Fe_1-xCu_xCr₂S₄(0.1lesxles0.5) 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 (Cr³⁺) and monovalent (Cu⁺), respectively. The Fe 2p XAS spectra of Fe_1-xCu_xCr₂S₄ 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_g states of Fe 3d electrons are located very close to E_F, suggesting that the hybridized Fe e_g-S 3p states near E_F play an important role in determining the transport properties of Fe_1-xCu_xCr₂S₄ for xles0.5.