Density functional theory calculations indicated that the incorporation of V into Ti lattice positions of rutile led to magnetic V4+ species, but the extension and sign of the coupling between dopant moments confirmed that ferromagnetic order cannot be reached via low-concentration doping in the non-defective oxide. Oxygen vacancies could introduce additional magnetic centres, and it was shown here that one of the effects of vanadium doping was to reduce the formation energies of these defects. In the presence of both V dopants and O vacancies all the spins tend to align with the same orientation. It was concluded that V-doping favoured the ferromagnetic behaviour of TiO2 not only by introducing spins associated with the dopant centres but also by increasing the concentration of oxygen vacancies with respect to the pure oxide.

The Interplay between Dopants and Oxygen Vacancies in the Magnetism of V-Doped TiO2. Grau-Crespo, R., Schwingenschlögl, U.: Journal of Physics - Condensed Matter, 2011, 23[33], 334216