Intrinsic defects in multiferroic BiFeO3 and their effect on magnetism

We investigate the energetics of the intrinsic defects in bulk multiferroic BiFeO3 and explore their implication for magnetization using a first-principles approach based on density functional theory. We find that the dominant defects in oxidizing (oxygen-rich) conditions are Bi and Fe vacancies and in reducing (oxygen-poor) conditions are O and Bi vacancies. The calculated carrier concentration shows that the BiFeO3 grown in oxidizing conditions has p-type conductivity. The conductivity decreases with oxygen partial pressure, and the material becomes insulating with a tendency for n-type conductivity. We find that the Bi and Fe vacancies produce a magnetic moment of similar to 1 mu B and 5 mu B per vacancy, respectively, for p-type BiFeO3 and none for insulating BiFeO3. O vacancies do not introduce any moment for both p-type and insulating BiFeO3. Calculated magnetic moments due to intrinsic defects are consistent with those reported experimentally for bulk BiFeO3.