Intrinsic Ferromagnetism in Insulating Cobalt Doped AnataseTiO2

Using complementary experiments we show that the room temperature ferromagnetism observed in anatase $\mathrm{Co}:{\mathrm{TiO}}_2$ 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 $M_{\mathrm{S}}$ of $1.1{\mu }_{\mathrm{B}}/\mathrm{Co}$ atom, while all films are highly insulating. The evidence of intrinsic ferromagnetism in the dielectric ground state of $\mathrm{Co}:{\mathrm{TiO}}_2$ leads to new considerations for the origin of ferromagnetism in transition metal doped oxides.