Tunable magnetic anisotropy in multiferroic oxides

Room-temperature electric-field control of magnetism is actively sought to realize electric-field assisted changes in perpendicular magnetic anisotropy (PMA), which is important to magnetic random access memories (MRAMs) and future spin-orbit based logic technologies. Traditional routes to achieve such control rely on heterostructures of ferromagnets and/or ferroelectrics, exploiting interfacial effects, including strain generated by the substrate, or electric-field induced changes in the interfacial electronic structures. Here we present design rules based on d-orbital splitting in an octahedral field and crystallographic symmetries for electric-field control of PMA utilizing hybrid improper ferroelectricity by scaffolding simple perovskite oxides into ultrashort period superlattices, (ABO3)1/(A′BO3)1, and in multiferroic AA′BB′O6 double perovskites. We validate the strategy using first principles calculations and a single-ion anisotropic model. We find a change in the magnetic anisotropy from the in-plane to the out of plane direction in (BiFeO3)1/(LaFeO3)1 and a 50% decrease of the magnetization along the out of plane direction in LaYNiMnO6, when a polar to nonpolar phase transition occurs with strain. The origin of the PMA control is due to the structural tunable competitions among the t2g and eg orbital interactions on the magnetic ions arising from relativistic spin-orbital interactions that are susceptible to changes in the oxygen octahedral tilts across the field-tunable transition. Our results allow us to search rapidly for other promising multiferroics materials with voltage-controlled magnetic anisotropy for applications in low-energy information storage and logic devices.