Epitaxial phases of BiMnO₃ from first principles

Authors

O. Diéguez and J. Íñiguez

Reference

Physical Review B, vol. 91, no. 18, p. 184113, 2015

Description

BiMnO₃ is the only transition-metal perovskite oxide that is insulating and shows strong ferromagnetism in bulk. This distinctive behavior would make it a promising candidate as a magnetoelectric multiferroic if it was also a polar material, but experiments have shown that bulk BiMnO₃ has either a very small polarization (below 0.1μC/cm²) or, most likely, that it is a paraelectric. There is also experimental evidence that the polarization in BiMnO₃ films grown on SrTiO₃ can be as high as 20μC/cm². Despite the interest in these behaviors, the diagram of BiMnO₃ as a function of epitaxial strain has remained largely unexplored. Here, we use first-principles to predict that, both under enough compressive and tensile epitaxial strain, BiMnO₃ films are ferroelectric with a giant polarization around 100μC/cm². The phases displayed by the films are similar to those experimentally found for BiFeO₃ in similar conditions—at compressive strains, the film is supertetragonal with a large component of the polarization pointing out of plane, while at tensile strains the polarization points mostly in plane. As in BiFeO₃ films, these phases are antiferromagnetic—the orbital ordering responsible for ferromagnetism in BiMnO₃ is absent in the polar phases. Our calculations also show that the band gap of some of these BiMnO₃ films is substantially smaller than gaps typically found in ferroelectric oxides, suggesting it may be a suitable material for photovoltaic applications.

Link

doi:10.1103/PhysRevB.91.184113