Ferromagnetic spin coupling of 2p-impurities in band insulators   stabilized by intersite Coulomb interaction: Nitrogen-doped MgO
  For a nitrogen dimer in insulating MgO, a ferromagnetic coupling between spin-polarized $2p$-holes is revealed by calculations based on the density functional theory amended by an on-site Coulomb interaction and corroborated by the Hubbard model. It is shown that the ferromagnetic coupling is facilitated by a T-shaped orbital arrangement of the $2p$-holes, which is in its turn controlled by an intersite Coulomb interaction due to the directionality of the $p$-orbitals. We thus conjecture that this interaction is an important ingredient of ferromagnetism in band insulators with $2p$ dopants. 
Ivetta Slipukhina, Phivos Mavropoulos, Stefan Bl\"ugel, and Marjana   Le\v{z}ai\'c
cond-mat.mtrl-sci