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

Several 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 sample, which has been probed by means of XAS and x-ray magnetic circular dichroism (XMCD) over several years. We find a mixed valent Fe²⁺, Fe³⁺ state, which shifts toward Fe³⁺ with time. An understanding of such a chemical change is of importance for potential applications of Sr₂FeMoO₆ and related transition metal oxides. [ABSTRACT FROM AUTHOR]