Intrinsic Ferromagnetism in Insulating Cobalt Doped Anatase TiO2

Using complementary experiments we show that the room temperature ferromagnetism observed in anatase Co:TiO 2 films is not carrier mediated, but coexists with the dielectric state. TEM and x-ray absorption spectroscopy reveal a solid solution of Co in anatase, where Co is not metallic but in the +2 state substituting for Ti. Measurements at 300 K yield a M s of 1.1 µ B /Co atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of Co:TiO 2 leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.