Effect of oxygen and magnesium vacancies on the d0 magnetism of C-monodoped MgO using ab initio method

The energetics, electronic structure and magnetism of C-monodoped MgO are investigated using first-principles GGA + U calculations. The results reveal that C induces magnetism in MgO when doped at the O and interstitial sites but becomes nonmagnetic when doped at Mg site. The calculated defect formation energies show that C prefers the Mg site as compared with the O and interstitial sites under O-rich condition. The interaction of native defects (Mg and O vacancies) with dopant C is well studied in detail and their magnetic coupling are discussed in terms of electronic structures and spin densities. It is found that the native defect play an important role on the magnetism formation of C-monodoped MgO system. In agreement with previous experimental works, the Mg vacancy mostly can promote the magnetism formation of C-anion-doped MgO system, and the O vacancy mostly can suppress the magnetism formation. However, when the native defect and dopant C are nearest neighbor, the Mg vacancy will weaken the magnetism formation and the O vacancy will completely suppress the magnetism formation. For C doped the interstitial site, in presence of Mg vacancy completely suppresses but not promotes the magnetism formation. For the C doped the interstitial site in presence of O vacancy, the defect system has lower defect formation energy compared with the one in absence of O vacancy and still holds stable magnetism. Our results indicate that the magnetism of MgO with composite defect is a common outcome of Hund's coupling, hybridization, Jahn-Teller distortion and compensating effect.