First-principles calculations were performed in order to understand the origin of magnetism in undoped GaN thin films. The results showed that the Ga vacancy, rather than that of N, contributed the observed magnetism, and that the magnetic moments came mainly from the unpaired 2p electrons at nearest-neighbour N atoms of the Ga vacancy. The calculations were also extended to bare and passivated GaN nanowires. It was found that a Ga vacancy on surface sites produced a total magnetic moment of 1.0μB while one within 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. Surface passivation by hydrogen was shown to enhance the ferromagnetism strongly. This theoretical study not only demonstrated that GaN nanowires could be magnetic, even without transition-metal doping, but also suggested that introducing a Ga vacancy was a natural and an effective means of fabricating 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