Photoemission, soft x-ray absorption, and magnetic circular dichroism spectroscopy study of Fe1-xCuxCr2S4 (0.1 ≤ x ≤ 0.5) spinel sulfides

The electronic and magnetic structures of Fe1-xCuxCr2S4 (0.1 <= x <= 0.5) spinel sulfides have been investigated systematically by performing photoemission spectroscopy (PES), soft x-ray absorption spectroscopy (XAS), and soft x-ray magnetic circular dichroism (XMCD) measurements using synchrotron radiation. Cr and Cu ions are found to be nearly trivalent (Cr3+) and monovalent (Cu+), respectively, and their valence states do not change with x. The Fe 2p XAS spectra of Fe1-xCuxCr2S4 are very similar to that of Fe metal, indicating that the Fe 3d electrons are strongly hybridized to other valence electrons. The Fe and Cr 2p XMCD spectra show that the magnetic moments of Cr ions and Fe ions are aligned antiparallel to each other and that both the Cr and Fe magnetic moments increase with increasing x. The valence-band PES study reveals that the Cr3+ (t(2g)(3) down arrow) 3d states are located at similar to 1.5 eV below E-F. The occupied Fe 3d states consist of the broad t(2g)(3) up arrow states, the e(g)(2) up arrow. states at similar to 4 eV below E-F, and the e(g) down arrow states very close to E-F. The filled Cu 3d(10) states lie at similar to 2.5 eV below E-F. This study suggests that the hybridized Fe e(g) down arrow and S 3p states near E-F play an important role in determining the transport properties of Fe1-xCuxCr2S4 for x <= 0.5.