Does the Self-Trapped Magnetic Polaron Exist in Electron-Doped Manganites?

We show from ab initio density-functional calculations and model studies that, in the electron-doped manganite LaₓCa_1-xMnO₃ (x1), unbound electrons are introduced into the conduction band, which then trap themselves in the exchange-induced magnetic potential wells forming the self-trapped magnetic polarons (STMP). Hopping beyond the nearest neighbors drastically reduces the binding energy, while the Jahn-Teller coupling increases it somewhat, resulting in a net binding of about 100±20 meV. The electron is self-trapped in a seven-site ferromagnetic region, beyond which the lattice is essentially antiferromagnetic. In light of the recent experiments of Neumeier and Cohn, our results suggest that the STMP may be present in the lightly electron-doped manganites.