First-principles study of magnetism driven by intrinsic defects in MgO

The d0 ferromagnetism of MgO containing neutral point defects has been investigated using the first-principles method. The generalized gradient approximation (GGA), local density approximation (LDA) and local density approximation with on-site effect UU (LDA+U  ) schemes were employed to describe the exchange correlation energy. Undoped MgO is found to be nonmagnetic. Neutral oxygen vacancies in the supercell induce no ferromagnetism, while neutral Mg vacancies could bring about large magnetic moments. The spin polarization of 2p electrons of oxygen atoms is responsible for the induced magnetic moments. The ferromagnetic moments enhance with an increase of the concentration of VMg0 vacancies. Ferromagnetism depends sensitively on the distribution of Mg vacancies. There may be a preferable occupation for VMg0 vacancies in the MgO lattice. The LDA+U   calculation indicates that a concentration of 6.25% VMg0 vacancies could convert the MgO insulator to half-metal. Our results may be valid for the region near the surface of nanograins.