Ferromagnetism of undoped GaN mediated by through-bond spin polarization between nitrogen dangling bonds

Room-temperature ferromagnetism occurs in GaN nanoparticles even without any doped magnetic ions. The cause for this finding was examined by performing density functional calculations for the bulk GaN and the nonpolar surface of GaN with Ga- and N-vacancies. Our work indicates that the room-temperature ferromagnetism of undoped GaN nanoparticles originates from the nitrogen dangling bonds associated with the surface Ga-vacancies. The spins of the nitrogen dangling bonds couple ferromagnetically by through-bond spin polarization, and this ferromagnetic coupling is effective even when the vacancy separation is as long as similar to 8 A.