Near Room‐Temperature Ferromagnetic Phase Achieved in 4 <i>d</i> Ruthenate via Interfacial Ferrimagnetic Coupling and Octahedral Rotation Engineering

Transition metal oxides (TMOs) simultaneously possessing strong spin-orbit coupling, near room-temperature ferromagnetism, and excellent conductivity are scarce while they show great potential applications in oxide spintronics. Here, a TMO with all these features is reported, existing as an interfacial phase in the 4d Ca_0.5Sr_0.5RuO₃ layer sandwiched by two LaMnO₃ layers. This phase is well conductive and ferromagnetic in a wide temperature range, with the highest Curie temperature of ≈275 K among the 4d/5d-TMOs. Particularly, this interfacial phase shows a considerably improved saturation magnetization (≈2 µ_B/Ru, twice that of the bulk counterpart), and a greatly reduced coercive force. All these features are highly desired by the application of spin-orbit torque. Due to the presence of strong spin-orbit coupling, such a Ca_0.5Sr_0.5RuO₃ interfacial phase exhibits a significantly larger anomalous Hall conductivity than the typical 3d oxide ferromagnet La_2/3Sr_1/3MnO₃ near room temperature. Analyses based on the techniques of X-ray magnetic circular dichroism, polarized-neutron reflectometry, and scanning transmission electron microscopy reveal a magnetic exchange interaction between the interfacial phases of Ca_0.5Sr_0.5RuO₃ and LaMnO₃ and an obvious expansion of the interfacial Mn─O─Mn bond angle, stabilizing the high-temperature ferromagnetic state of the CSRO/LMO interface.