Symmetry-Mismatch-Induced Ferromagnetism in the Interfacial Layers of CaRuO3/SrTiO3 Superlattices

By modifying the entangled multi-degrees of freedom of transition-metal oxides, interlayer coupling usually produces interfacial phases with unusual functionalities. Herein, a symmetry-mismatch-driven interfacial phase transition from paramagnetic to ferromagnetic state is reported. By constructing superlattices using CaRuO3 and SrTiO3, two oxides with different oxygen octahedron networks, the tilting/rotation of oxygen octahedra near interface is tuned dramatically, causing an angle increase from approximate to 150 degrees to approximate to 165 degrees for the Ru-O-Ru bond. This in turn drives the interfacial layer of CaRuO3, approximate to 3 unit cells in thickness, from paramagnetic into ferromagnetic state. The ferromagnetic order is robust, showing the highest Curie temperature of approximate to 120 K and the largest saturation magnetization of approximate to 0.7 mu(B) per formula unit. Density functional theory calculations show that the reduced tilting/rotation of RuO6 octahedra favors an itinerant ferromagnetic ground state. This work demonstrates an effective phase tuning by coupled octahedral rotations, offering a new approach to explore emergent materials with desired functionalities.