Realization of a ferromagnetic insulator in the La0.7Sr0.3MnO3/LaCoO3 superlattice

Artificially structured oxide superlattices provide a fertile ground for engineering electronic states. In this work, we report the synthesis of high-quality La0.7Sr0.3MnO3/LaCoO3 superlattices, which exhibit insulating ferromagnetism with a Curie temperature (TC) elevated to 230 K. Unlike conventional La0.7Sr0.3MnO3/SrTiO3 counterparts, the magnetic ordering in this system is driven by a distinct interfacial mechanism. By systematically varying the layer thickness, we observe a clear correlation between the ferromagnetic coupling and the interface density. Spectroscopic evidence from x-ray absorption identifies a valence shift toward the Co2+ state, indicative of Mn-to-Co charge transfer. This electronic reconstruction activates a strong superexchange pathway between Mn4+ and Co2+, consistent with Goodenough–Kanamori–Anderson rules. Furthermore, element-specific magnetic circular dichroism reveals robust magnetic moments on both sublattices, persisting well above 200 K. Our findings demonstrate that interfacial charge redistribution in superlattices is a viable route to overcome the low-TC limitations of ferromagnetic insulators.