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(1.5)Co(1.5)O4 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.