Dopants, Defects and Magnetism in Epitaxial CoxTi1-xO2-x Anatase
  We demonstrate that room-temperature ferromagnetism in epitaxial Co-doped TiO2 anatase is driven by electron-mediated exchange interaction, and not by metallic Co clusters. Co(II) substitutes for Ti(VI) in the lattice and produces oxygen vacancies that do not contribute carriers. Free electrons originate with oxygen vacancies resulting from an oxygen deficiency during growth. 
S.A. Chambers, S.M. Heald, R.F.C. Farrow, J.-U. Thiele, R.F. Marks,   M.F. Toney, A. Chattopadhyay