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Electronic and Magnetic Structure of the (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$ Superlattices

We study the magnetic structure of the (LaMnO$_3$)$_{2n}$/(SrMnO$_3$)$_n$ superlattices from density-functional calculations. In agreement with the experiments, we find that the magnetism changes with the layer thickness `n'. The reason for the different magnetic structures is shown to be the varying potential barrier across the interface, which controls the leakage of the Mn-e$_g$ electrons from the LMO side to the SMO side. This in turn affects the interfacial magnetism via the carrier-mediated Zener double exchange. For n=1 superlattice, the Mn-e$_g$ electrons are more or less spread over the entire lattice, so that the magnetic behavior is similar to the equivalent alloy compound La$_{2/3}$Sr$_{1/3}$MnO$_3$. For larger n, the e$_g$ electron transfer occurs mostly between the two layers adjacent to the interface, thus leaving the magnetism unchanged and bulk-like away from the interface region.