Half-Metallic Ferromagnetism in LaAlO$_3$/SrMnO$_3$ Nanosheet Superlattices

Based on first-principle density-functional theory, we have revealed a robust half-metallic ferromagnetism in LaAlO$_{3}$/SrMnO$_{3}$ nanosheet supperlattices. Interface electronic reconstruction, where electrons transfer from the (LaO)$^{+}$ layer to the adjacent (MnO$_{2})^{0}$ layer, is found to lead to the partially occupied e$_{g}$ orbitals at the Mn sites and the half-metallic state in nn-type superlattice via the Zener double-exchange mechanism. On the other hand, holes transfer from (AlO$_{2})^{-}$ layer to (SrO)$^{0}$ layer and reside mainly at oxygen sites in SrMnO$_{3}$, leading to either the preserved G-type AFM ordering in pp-type superlattices or complex magnetic ordering in np-type superlattices. When these systems transist to ferromagnetic ordering by an external magnetic field, an obvious change of electronic states at the Fermi level is found, suggesting a large magnetoresistive effect therein.