Room-Temperature Ferromagnetism with Strong Spin–Orbit Coupling Achieved in CaRuO3 Interfacial Phase via Magnetic Proximity Effect

Recently, theoretical and experimental research predicted that ferromagnets with strong spin–orbit coupling (SOC) could serve as spin sources with dramatically enhanced spin–orbit torque (SOT) efficiency due to the combination of spin Hall effect and anomalous Hall effect (AHE), presenting potential advantages over conventional nonmagnetic heavy metals. However, materials with a strong SOC and room-temperature ferromagnetism are rare. Here, we report on a ferromagnetic (FM) interfacial phase with Curie temperature exceeding 300 K in the heavy transition-metal oxide CaRuO₃, in proximity to La_0.67Sr_0.33MnO₃. Electron energy loss and polarized neutron reflectometry spectra reveal the strong charge transfer from Ru to Mn at the interface, triggering antiferromagnetic exchange interactions between interfacial Ru/Mn ions and thus transferring magnetic order from La_0.67Sr_0.33MnO₃ to CaRuO₃. An obvious advantage of such interfacial phase is the enhanced anomalous Hall effect at temperatures from 150 to 300 K. Compared to the most promising room-temperature ferromagnetic oxide La_0.67Sr_0.33MnO₃, the anomalous Hall conductivity σ_xy^AHE (or anomalous Hall angle θ_H) of CaRuO₃/La_0.67Sr_0.33MnO₃ superlattices is increased by 30 (or 31) times at 150 K and 10 (or 3) times at 300 K. This work demonstrates a special approach for inducing ferromagnetism in heavy transition-metal oxides with strong SOC, offering promising prospects for all-oxide-based spintronic applications.