Dimensional control of interface coupling-induced ferromagnetism in CaRuO3/SrCuO2 superlattices

Due to the strong interactions from multiple degrees of freedom at the interfaces, electron-correlated oxide heterostructures have provided a promising platform for creating exotic quantum states. Understanding and controlling the coupling effects at the oxide interface are prerequisites for designing emergent interfacial phases with desired functionalities. Here, we report the dimensional control of the interface coupling-induced ferromagnetic (FM) phase in perovskite-CaRuO₃/infinite-layered-SrCuO₂ superlattices. Structural analysis reveals the occurrence of chain-type to planar-type structural transitions for the SrCuO₂ layer as the layer thickness increases. The Hall and magnetoresistance measurements indicate the appearance of an interfacial FM state in the originally paramagnetic CaRuO₃ layers when the CaRuO₃ layer is in proximity to the chain-type SrCuO₂ layers; this superlattice has the highest Curie temperature of ~75 K and perpendicular magnetic anisotropy. Along with the thickness-driven structural transition of the SrCuO₂ layers, the interfacial FM order gradually deteriorates and finally disappears. As shown by the X-ray absorption results, the charge transfer at the CaRuO₃/chain-SrCuO₂ and CaRuO₃/plane-SrCuO₂ interfaces are different, resulting in dimensional control of the interfacial magnetic state. The results from our study can be used to facilitate a new method to manipulate interface coupling and create emergent interfacial phases in oxide heterostructures.