First-principles calculations were performed in order to understand the origin of magnetism in undoped GaN thin films. The results showed that Ga vacancy, rather than that of N contributed the observed magnetism, and the magnetic moments mainly come from the unpaired 2p electrons at nearest-neighbour N atoms of the Ga vacancy. Calculations and discussions were also extended to bare and passivated GaN nanowires, It was found that per Ga vacancy on the surface sites products the total magnetic moment of 1.0μB while that inside of the nanowires could lead to the formation of a net moment of 3.0μB. The coupling between two Ga vacancies was also studied and it was found that the coupling was ferromagnetic coupling. The surface passivation with hydrogen was shown to strongly enhance the ferromagnetism. This theoretical study not only demonstrated that GaN nanowire could be magnetic even without transition-metal doping, but also suggested that introducing Ga vacancy was a natural and an effective way to fabricate low-dimensional magnetic GaN nanostructures.

Ferromagnetism Driven by Cation Vacancy in GaN Thin Films and Nanowires. A.Kuang, H.Yuan, H.Chen: Applied Surface Science, 2010, 256[20], 6040-6