Magnetic order and valency at La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$/SrTiO${}_3$ interfaces

We report on first principles calculations of the electronic structure of La${}_{0.7}$Sr${}_{0.3}$MnO${}_3$/SrTiO${}_3$ junction with two possible types of interface terminations. We find that the La${}_{0.7}$Sr${}_{0.3}$O/TiO${}_2$ interface preserves the interlayer ferromagnetic coupling between the interface MnO${}_2$ layer and the bulk. The other interface, MnO${}_2$/SrO, favours antiferromagnetic coupling with the bulk. By inserting two unit cells of undoped LaMnO${}_3$ at the interface the ferromagnetism is recovered. This is understood in terms of the doping level and the mobility of carriers near the interface.