Using first-principles density functional calculations, An investigation was made of  the electronic structures of Ti-doped ZnO (Ti was in 4+ oxidation state) with and without oxygen vacancy. The ferromagnetic property was identified in the presence of oxygen vacancy despite Ti being nonmagnetic in its natural phase. The ferromagnetism originates from the charge transferring from donor derived-defect band to unoccupied Ti-3d states and the hybridization between Ti-3d and O-2p band near the Fermi level. On increasing the oxygen vacancy concentration, a transition from a long-ranged magnetic order to a short-ranged interaction was found and the oxygen vacancies prefer to distribute non-uniformly in Ti-doped ZnO.

First-Principles Study of Ferromagnetism in Ti-Doped ZnO with Oxygen Vacancy. Weng, Z., Huang, Z., Lin, W.: Physica B, 2012, 407[4], 743–7