Interface-induced magnetic polar metal phase in complex oxides

Abstract

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 BaTiO3/SrRuO3/BaTiO3 heterostructure. Electron microscopy reveals polar lattice distortions in three-unit-cells thick SrRuO3 between BaTiO3 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 SrRuO3 layer can be attributed to the effect of electrostatic carrier accumulation induced by the BaTiO3 layers. Density-functional-theory calculations provide insights into the origin of the observed properties of the thin SrRuO3 film. The present results pave a way to design materials with desired functionalities at oxide interfaces.

Defect‐Engineered Dzyaloshinskii–Moriya Interaction and Electric‐Field‐Switchable Topological Spin Texture in SrRuO3

“…In these systems, inversion‐symmetry‐breaking can be created via artificially designed SOC/ferromagnetic interface, [ 16,19 ] ferroelectric proximity effect, [ 17 ] octahedral distortion gradient, [ 20,21 ] and interfacial exchange bias. [ 22 ] In some cases, [ 17,19,21 ] the resultant DMI can strongly couple with multiple functionalities at the heterointerfaces, which can enable electrically tunable skyrmionic properties and THE, but the length‐scale of those interfacial DMI is limited within a few unit‐cells (ucs) only, [ 23–25 ] leading to small modulation amplitudes. In addition to these interface‐mediated scenarios, recent works further imply inhomogeneous proton intercalation and ion irradiation might be able to induce the THE in much thicker oxide films (>10 nm).…”

Free-Carrier-Induced Ferroelectricity in Layered Perovskites

“…The first observation of polarization switching in a ferroelectric (semi-)metal is even more recent [11,12]. The interest in polar and ferroelectric-like metals is continuing to increase in both bulk and heterostructures [13][14][15][16][17][18][19][20][21][22][23][24] and they continue to promise both a fertile playground for interesting emergent phenomena (including, but not limited to mixed singlet-triplet superconductivity [25] and novel optical effects [26]), and immediate relevance to applications as polar electrodes [27].…”

Asymmetric interfaces and high-TC ferromagnetic phase in La0.67Ca0.33MnO3/SrRuO3 superlattices

“…Both the ultrathin LCMO and SRO films with degraded metallicity cannot provide enough carriers to fully screen the unbalanced interfacial charges [48]. Hence, a ferroelectric-like polar distortion becomes energetically favorable to provide additional ionic screening [21,22,48,49].…”

“…For instance, charge transfer can induce an emergent ferromagnetic state at the CaRuO3/CaMnO3 and SrIrO3/SrMnO3 interfaces, while the bulk compounds are either paramagnetic or antiferromagnetic [19,20]. The interfacial proximity of polar distortion can give rise to skyrmion-like magnetic bubbles as well as a high-spin ferromagnetic state in SrRuO3 (SRO) [21,22]. And interfacial couplings of octahedral distortion in SRO/Ca0.5Sr0.5TiO3/GdScO3(110) heterostructure can result in a highly tunable magnetic anisotropy [23].…”