Percolative Ferromagnetism in Anatase Co:TiO2
  We revisit the most widely investigated and controversial oxide diluted magnetic semiconductor (DMS), Co:TiO2, with a new high temperature film growth, and show that the corresponding material is not only an intrinsic DMS ferromagnet, but also supports a percolative mechanism of ferromagnetism. We establish the uniformity of dopant distribution across the film cross section by Z-contrast imaging via scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) at spatial resolution of 0.4 nm and the oxidized 2+ valence state of cobalt by x-ray absorption spectroscopy (XAS). The dependence of magnetic properties on cobalt concentration is consistent with the defect polaron percolation model. The peculiar increase in the transport activation energy above a specific cobalt concentration further emphasizes the polaron contribution to magnetic order. 
S. R. Shinde, S. B. Ogale, Abhijit S. Ogale, S. J. Welz, A. Lussier,   Darshan C. Kundaliya, H. Zheng, S. Dhar, M.S.R. Rao, ...