Local Fe structure and ferromagnetism in Fe-doped ZnO films

The local Fe structure and corresponding ferromagnetism are different for various concentrations of Fe-doped ZnO (Zn1-xFexO, x = 0-0.07) films, which are prepared on LiNbO3(104) substrates by reactive magnetron sputtering. X-ray photoelectron spectroscopy and x-ray absorption near-edge structure (XANES) reveal that, when x < =0.04, Fe is in the 2+ state and is incorporated into the wurtzite lattice of ZnO, and as x increases further, a second phase Fe3O4 is induced. Furthermore, full multiple-scattering substitution ab initio calculation of Fe K-edge XANES is used to confirm the local structure of Fe in films with different x. The single-phase Fe-doped ZnO films (x < =0.04) exhibit ferromagnetism above room temperature and the mechanism of bound magnetic polarons (BMPs) is proposed to discuss the magnetic properties. The presence of the second phase is responsible for the strong ferromagnetism for higher Fe concentration.