High-temperature ferromagnetic LaCoO3 triggered by interfacial electron transfer and exchange coupling

The perovskite oxide heterointerface is a complex and fascinating region where charge transfer dramatically alters the coupling between charge, spin, orbital, and lattice order, resulting in novel phenomena absent in bulk materials. Understanding and controlling these interfacial effects is crucial for designing and optimizing oxide heterostructures for potential applications. Specifically, charge transfer can stabilize and enhance the ferromagnetic order at the interface, effectively improving the properties of magnetic materials. In this work, a detailed investigation of the $\mathrm{LaCo}{\mathrm{O}}_{3}/\mathrm{L}{\mathrm{a}}_{2/3}\mathrm{S}{\mathrm{r}}_{1/3}\mathrm{Mn}{\mathrm{O}}_{3}$ heterostructures revealed Mn-Co ferromagnetic coupling induced by charge transfer at the interface. Remarkably, this interfacial ferromagnetic coupling dramatically increased the Curie temperature of the $\mathrm{LaCo}{\mathrm{O}}_{3}$ film up to 190 K, which is significantly higher than the single $\mathrm{LaCo}{\mathrm{O}}_{3}$ film. Using surface-sensitive x-ray absorption spectra and x-ray magnetic circular dichroism, we find sizable $\mathrm{C}{\mathrm{o}}^{2+}$ forms from the charge transfer between Mn-Co sites at the interface. Combined with density functional theory calculations, it is clear that the ${e}_{g}{}^{0}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}{e}_{g}{}^{2}$ type $\mathrm{M}{\mathrm{n}}^{4+}\text{\ensuremath{-}}\mathrm{O}\text{\ensuremath{-}}\mathrm{C}{\mathrm{o}}^{2+}$ superexchange interaction is at the root of the strong ferromagnetic coupling behavior. This work demonstrates that interface modulation in perovskite heterostructures can be a powerful tool for manipulating overall magnetism. It also underscores that perovskite oxide interfaces provide an ideal platform for exploring intricate interactions between different order parameters and inducing novel interfacial effects.