Improved multiferroic behavior in [111]-oriented BiFeO₃/ BiAlO₃ superlattice

We report a systematic study on the structural, electronic, magnetic, and ferroelectric properties of [111]-oriented BiFeO₃/BiAlO₃ (BFO/BAO) superlattice using density-functional calculations. It is found that the Fe-O-Fe superexchange interactions in BFO/BAO superlattice are greatly suppressed by the inserted BAO layers, with the antiferromagnetic-ferromagnetic transition energy decreasing from around 280 meV per BFO formula unit (five atoms) to 11.6 meV per BFO/BAO formula unit (ten atoms). The tensile strain can further decrease this energy, making the magnetic transition more plausible. In addition, we find that BFO/BAO superlattice preserves the large ferroelectric polarization as well as energy gap of bulk BFO. Therefore, BAO may be a good candidate for constructing the BFO-based superlattice with improved multiferroicity.