X-ray magnetic circular dichroism in cobalt-iron spinels and electronic states of Co ions

Synchrotron X-ray experiments on magnetic circular dichroism (XMCD) have been performed at Co K and Fe K absorption edges for CoFe₂O₄, Fe_1.5Co_1.5O₄ and FeCo₂O₄ with the spinel structure. The XANES studies have clarified that only Fe³⁺ exists in all compounds and Co²⁺ and Co³⁺ coexist in the latter two cobaltites. A systematic change in XMCD spectra has concluded that the Co²⁺ ions in the B sites of FeCo₂O₄ are in the low-spin state. Since the Co²⁺ ions in CoFe₂O₄ are in the high-spin state, the spectra of the intermediate cobaltite may be explained as a mixture of low-spin and high-spin states.