Fe valence state of Sr2FeMoO6 probed by x-ray absorption spectroscopy: the sample age matters

Recent studies of the magnetic properties of Sr2FeMoO6, a half metallic double perovskite showing large magneto resistance effects at room temperature, by means of site specific x-ray absorption spectroscopy (XAS) have led to very different results concerning the Fe valence state. We present a detailed study of a Sr2FeMoO6 polycrystalline sample, which has been probed by means of XAS and XMCD over several years. We find a mixed valent Fe2+, Fe3+ state, which shifts towards Fe3+ with time. An understanding of such a chemical change is of importance for potential applications of Sr2FeMoO6 and related transition metal oxides.