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

Several studies of the magnetic properties of Sr(2)FeMoO(6), 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 Sr(2)FeMoO(6) sample, which has been probed by means of XAS and x-ray magnetic circular dichroism (XMCD) over several years. We find a mixed valent Fe(2+), Fe(3+) state, which shifts toward Fe(3+) with time. An understanding of such a chemical change is of importance for potential applications of Sr(2)FeMoO(6) and related transition metal oxides. (C) 2008 American Institute of Physics.