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

Abstract 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 4 d Ca _0.5 Sr _0.5 RuO ₃ layer sandwiched by two LaMnO ₃ layers. This phase is well conductive and ferromagnetic in a wide temperature range, with the highest Curie temperature of ≈275 K among the 4 d /5 d ‐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 _0.5 Sr _0.5 RuO ₃ interfacial phase exhibits a significantly larger anomalous Hall conductivity than the typical 3 d oxide ferromagnet La _2/3 Sr _1/3 MnO ₃ 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 _0.5 Sr _0.5 RuO ₃ and LaMnO ₃ and an obvious expansion of the interfacial Mn─O─Mn bond angle, stabilizing the high‐temperature ferromagnetic state of the CSRO/LMO interface.