Role of O defects at the BiMnO₃/SrTiO₃ interface

We use first principles calculations to study ideal and O deficient BiMnO₃/SrTiO₃ superlattices. The ideal superlattice is characterized by parallel alignment of the Mn and Ti magnetic moments at the n-interface, while an antiparallel alignment has been reported experimentally. O defects at the n-interface are found to favor the MnO₂ and BiO layers over the TiO₂ layer. The band gap of the superlattice is strongly reduced when the MnO₂ layer is O deficient and states are observed at the Fermi energy when the BiO layer is O deficient. Only in the latter case the Mn and Ti magnetic moments at the n-interface align antiparallel. Therefore, O defects in the BiO layer turn out to be essential for reproducing the experimental interface magnetism and for understanding its mechanism.