Ferromagnetism in Fe-doped $SnO2$ thin films

Thin films grown by pulsed-laser deposition from targets of $Sn0.95Fe0.05O2$ are transparent ferromagnets with Curie temperature and spontaneous magnetization of 610 K and $2.2 A m2 kg−1,$ respectively. The $Fe57$ Mössbauer spectra show the iron is all high-spin $Fe3+$ but the films are magnetically inhomogeneous on an atomic scale, with only 23% of the iron ordering magnetically. The net ferromagnetic moment per ordered iron ion, $1.8 μB,$ is greater than for any simple iron oxide with superexchange interactions. Ferromagnetic coupling of ferric ions via an electron trapped in a bridging oxygen vacancy $(F$ center) is proposed to explain the high Curie temperature.