Interstitial-nitrogen- and oxygen-induced magnetism in Gd-doped GaN

The observed ferromagnetism in Gd-doped GaN appears 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 is 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 are 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 are also energetically attracted toward the Gd and energetically more likely to form in the presence of Gd.