Interface-induced magnetic polar metal phase in complex oxides

Polar metals are commonly defined as metals with polar structural distortions. Strict symmetry restrictions make them an extremely rare breed as the structural constraints favor insulating over metallic phase. Moreover, no polar metals are known to be magnetic. Here we report on the realization of a magnetic polar metal phase in a BaTiO 3 /SrRuO 3 /BaTiO 3 heterostructure. Electron microscopy reveals polar lattice distortions in three-unit-cells thick SrRuO 3 between BaTiO 3 layers. Electrical transport and magnetization measurements reveal that this heterostructure possesses a metallic phase with high conductivity and ferromagnetic ordering with high saturation moment. The high conductivity in the SrRuO 3 layer can be attributed to the effect of electrostatic carrier accumulation induced by the BaTiO 3 layers. Density-functional-theory calculations provide insights into the origin of the observed properties of the thin SrRuO 3 film. The present results pave a way to design materials with desired functionalities at oxide interfaces. Polar metals—metals with polar structural distortions—are known not to be magnetic. Here, the authors demonstrate a magnetic polar metal phase in a BaTiO 3 /SrRuO 3 /BaTiO 3 heterostructure displaying high conductivity and ferromagnetic ordering with high saturation moment.