The dependencies on strain and O vacancies of the ferroelectric polarization and the weak ferromagnetic magnetization in the multiferroic material bismuth ferrite, BiFeO3, were investigated by using first principles density functional theory calculations. The electric polarization was found to be rather independent of strain, in striking contrast to most conventional perovskite ferroelectrics. It was also not significantly affected by O vacancies, or by the combined presence of strain and O vacancies. The magnetization was also unaffected by strain, however, the incorporation of O vacancies could alter the magnetization slightly, and also leads to the formation of Fe2+. These results were considered in the light of recent experiments on epitaxial films of BiFeO3, which reported a strong thickness dependence of both magnetization and polarization.

Influence of Strain and Oxygen Vacancies on the Magneto-Electric Properties of Multiferroic Bismuth Ferrite. C.Ederer, N.A.Spaldin: Physical Review B, 2005, 71[22], 224103 (9pp)