Asymmetric interfaces and high-T_C ferromagnetic phase in La_0.67Ca_0.33MnO₃/SrRuO₃ superlattices

Interfacial magnetism in functional oxide heterostructures not only exhibits intriguing physical phenomena but also implies great potential for device applications. In these systems, interfacial structural and electronic reconstructions are essential for improving the stability and tunability of the magnetic properties. In this work, we constructed ultra-thin La_0.67Ca_0.33MnO₃ (LCMO) and SrRuO₃ (SRO) layers into superlattices, which exhibited a robust ferromagnetic phase. The high Curie temperature (T_C) reaches 291 K, more than 30 K higher than that of bulk LCMO. We found that the LCMO/SRO superlattices consisted of atomically-sharp and asymmetric heterointerfaces. Such a unique interface structure can trigger a sizable charge transfer as well as a ferroelectric-like polar distortion. These two interfacial effects cooperatively stabilized the high-T_C ferromagnetic phase. Our results could pave a promising approach towards effective control of interfacial magnetism and new designs of oxide-based spintronic devices.