Ferromagnetic spin coupling of 2p-impurities in band insulators stabilized by intersite Coulomb interaction: Nitrogen-doped MgO

TL;DR

This paper demonstrates that intersite Coulomb interactions enable ferromagnetic coupling between nitrogen-induced 2p holes in MgO, revealing a new mechanism for ferromagnetism in band insulators with p-dopants.

Contribution

It introduces a novel understanding of ferromagnetism in band insulators through the role of intersite Coulomb interactions and orbital arrangements of 2p dopants.

Findings

Ferromagnetic coupling between nitrogen 2p holes in MgO is confirmed.

Intersite Coulomb interaction controls the orbital arrangement facilitating ferromagnetism.

The mechanism may be relevant for other p-doped band insulators.

Abstract

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.