Magnetic properties of Mn-doped GaN with defects: ab-initio calculations

According to first-principles density functional calculations, we have investigated the magnetic properties of Mn-doped GaN with defects, Ga_1-x-yV_GxMn_y N_1-z-tV_NzO_t with Mn substituted at Ga sites, nitrogen vacancies V_N, gallium vacancies V_G and oxygen substituted at nitrogen sites. The magnetic interaction in Mn-doped GaN favours the ferromagnetic coupling via the double exchange mechanism. The ground state is found to be well described by a model based on a Mn³⁺—d⁵ in a high spin state coupled via a double exchange to a partially delocalized hole accommodated in the 2p states of neighbouring nitrogen ions. The effect of defects on ferromagnetic coupling is investigated. It is found that in the presence of donor defects, such as oxygen substituted at nitrogen sites, nitrogen vacancy antiferromagnetic interactions appear, while in the case of Ga vacancies, the interactions remain ferromagnetic; in the case of acceptor defects like Mg and Zn codoping, ferromagnetism is stabilized. The formation energies of these defects are computed. Furthermore, the half-metallic behaviours appear in some studied compounds.