Density-functional Study of Suppressed Magnetism at La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ Interfaces*

The experimentally observed magnetism suppression at interfaces of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ has attracted increasing attention. Here we report density-functional calculations for the interface systems of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$. Two interface models are employed to isolate and identify different effects coming from epitaxial strain, symmetry-breaking, charge redistribution, and oxygen vacancy segregation. We found that the strain effect from SrTiO$_{3}$ substrate is not significant enough to cause magnetism suppression at the interface. Although the symmetry is broken at interfaces, this effect leads only to a local ground state and does not cause the observed suppression either. The choice of interface termination does have an effect: moderate magnetism suppression is found for SrO/MnO$_{2}$ termination. Finally, we considered the effect of oxygen vacancy segregation at the interface. In the scenarios we have tested, oxygen vacancies do not suppress the interfacial magnetism. Thus, a complicated mechanism is needed to explain the suppressed magnetism at La$_{0.7}$Sr$_{0.3}$MnO$_{3}$/SrTiO$_{3}$ interfaces.