The observed ferromagnetism in Gd-doped GaN appeared to arise from lattice defects incorporated along with Gd rather than from Gd itself. A previous model, invoking Ga vacancies as the primary defect responsible for the magnetism was here argued to be unlikely because Ga vacancies have a high energy of formation in the neutral charge state that carries magnetic moment. Interstitial nitrogen as well as oxygen in octahedral sites next to Gd were shown to be a more likely source of defect induced magnetism. They not only support magnetic moments and ferromagnetic coupling in semi-insulating conditions but were also energetically attracted toward the Gd and energetically more likely to form in the presence of Gd.

Interstitial-Nitrogen- and Oxygen-Induced Magnetism in Gd-Doped GaN. C.Mitra, W.Lambrecht: Physical Review B, 2009, 80[8], 081202