Orbital reconstruction and interface ferromagnetism in self-assembled nanosheet superlattices.

We have investigated the interface electronic states in self-assembled (Ti(0.8)Co(0.2)O(2)/Ti(0.6)Fe(0.4)O(2))(n) superlattices by X-ray photoelectron spectroscopy. A charge of about -0.3 electron is transferred from Fe to Co ions across the interface and induces a major reconstruction of the orbital occupation at the interfacial (Ti(0.8)Co(0.2)O(2)/Ti(0.6)Fe(0.4)O(2)) layers. Supported by first-principles calculations, the Co(3+) state is partially occupied at the interface by superlattice formation, and this new magnetic state directly influences the coupling between Ti(0.8)Co(0.2)O(2) and Ti(0.6)Fe(0.4)O(2) nanosheets. These data indicate that the orbital reconstruction is indeed realized by the interface charge transfer between Co and Fe ions in the adjoined nanosheets, and the generic feature of engineered interfaces can be extended to self-assembled superlattices of oxide nanosheets.