Impact of interfacial coupling of oxygen octahedra on ferromagnetic order in LaSrMnO/SrTiO heterostructures.

LaSrMnO, a half-metallic ferromagnet with full spin polarization, is generally used as a standard spin injector in heterostructures. However, the magnetism of LaSrMnO is strongly modified near interfaces, which was addressed as "dead-layer" phenomenon whose origin is still controversial. Here, both magnetic and structural properties of LaSrMnO/SrTiO heterostructures were investigated, with emphasis on the quantitative analysis of oxygen octahedral rotation (OOR) across interfaces using annular-bright-field imaging. OOR was found to be significantly altered near interface for both LaSrMnO and SrTiO, as linked to the magnetism deterioration. Especially in LaSrMnO/SrTiO superlattices, the almost complete suppression of OOR in 4 unit-cell-thick LaSrMnO results in a canted ferromagnetism. Detailed comparisons between strain and OOR relaxation and especially the observation of an unexpected LaSrMnO lattice c expansion near interfaces, prove the relevance of OOR for the magnetic properties. These results indicate the capability of tuning the magnetism by engineering OOR at the atomic scale.