First-principles analysis of ferromagnetism in hexagonal and rhombohedral BN

In view of experimental reports of ferromagnetic behaviors in the as-prepared defective BN, the effect of B and N vacancies on the magnetic properties and electronic structure of h-BN and r-BN are investigated using first-principles calculations within the generalized gradient approximation (GGA) and GGA+U scheme. The B and N vacancy induces a set of spin-polarized defect states above the valence band and below the conduction band, respectively, resulting in the formation of local magnetic moment. It is noticed that the U correction for 2p electrons plays important role in obtaining spin-polarized ground states of the h-BN and r-BN systems with B vacancy. Furthermore, the magnetic coupling between the moments induced by two B vacancies is long-range ferromagnetic and the coupling can be attributed to the p-p hybridization interaction involving holes, whereas the coupling between the moments induced by two N vacancies is anti-ferromagnetic. The calculated results suggest that the observed d0 ferromagnetism in the as-prepared defective BN should be attributed to the B vacancies.