Origin of unexpected magnetism in Cu-doped TiO₂

Cu-doped TiO₂ has recently been found to exhibit unexpected room temperature ferromagnetism. In the present work, possible defect structures and the associated magnetism are calculated within the generalized gradient approximation using the projector augmented wave method (PAW). In particular, structures of the vacancy-Cu impurity complex are studied. Our results show that the magnetism is caused by: 1) the hybridization of p-d orbitals between the Cu and O ions, and 2) the spin polarization of the 3d orbital of Cu and of the 2p orbital of O ions.