Investigation of the valence states of Fe and Co in Fe1-xCoxOy (0 < x < 1) thin films by x-ray absorption spectroscopy

The unusual magnetic properties of thin films of Fe(1-x)Co(x)O(y) {0 <= x <= 1} ferrite solid solutions have been explained through an investigation of their electronic structure. The x-ray absorption near-edge structure (XANES) spectra of the Fe L(3)- edge and K-edges show that Co replaces Fe(3+) in the tetrahedral (T(d)) sites up to x = 0.34 and octahedral (Oh) sites from 0.39 < x < 0.89. The Co L(3)-edge and O K- edge results indicate mixed valence states of Co as it replaces Fe at dissimilar sites. From the results, it is concluded that the magnetic properties of the thin films of the spinel Fe(1-x)Co(x)O(y) arise from the Fe(3+) at the Td sites. The replacement of Fe(3+) and Fe(2+) by Co at the Oh sites results in a crossover to the rocksalt structure and a loss of the magnetic properties.