Improving Multiferroic Functionalities via Interface Engineering

By first-principles calculation, we show that the multiferroic properties of (SrMnO3)1/(SrCoO3)1 superlattices are significantly improved compared with epitaxially strained SrMnO3 and SrCoO3 thin films. A ferroelectric ferromagnetic insulator is achieved at a relatively small tensile strain of +1.80% instead of +3.40% for pure SrMnO3. The mean-field-estimated critical temperature TC is enhanced to above room temperature instead of 92 K for SrMnO3. This is made possible because a rich variety of oxygen octahedral tilting patterns across the SrMnO3/SrCoO3 interfaces facilitate the ferromagnetic superexchange coupling between Co and Mn ions. As Mn and Co ions participate in both magnetic moment formation and polar distortion, strong magnetoelectric coupling is therefore anticipated. Our study suggests that a suitable choice of superlattice constituents not only allows one to optimize the multiferroic functionalities, but also offers a platform to investigate the specific mechanism involved in the multiferroicity of transition-metal oxides.