First-principles calculations and Bader analysis of oxygen-deficient induced magnetism in cubic BaTiO3-x and SrTiO3-x

The possibility of oxygen deficient induced magnetism in cubic BaTiO3 (BTO) and SrTiO3 (STO) perovskites is investigated by first-principles calculations, using the projector-augmented-wave method, within the generalised gradient approximation (GGA) and generalised gradient approximation with on-site effect (GGA + U), for the exchange correlation potential. For non-stoichiometric BaTiO3-x and SrTiO3-x, supercells were created in order to have two vacancy concentrations, i.e. x = 0.125, 0.083. Spin charge distributions and magnetic moments associated with each ion, including local density of states projected in Bader atoms, were analysed by performing a full Bader charge analysis. Results show that oxygen vacancies could induce magnetism in BaTiO3-x with x = 0.125 and x = 0.083 under GGA and GGA + U approximations. For SrTiO3-x with x = 0.125, ferromagnetism is induced with GGA, whereas with GGA + U the non-magnetic state is retained. On the other hand, with x = 0.083, ferromagnetism is induced under GGA and GGA + U.