Impact of interfacial coupling of oxygen octahedra on ferromagnetic order in La0.7Sr0.3MnO3/SrTiO3heterostructures

Abstract

La0.7Sr0.3MnO3, a half-metallic ferromagnet with full spin polarization, is generally used as a standard spin injector in heterostructures. However, the magnetism of La 0.7 Sr0.3 MnO3 is strongly modified near interfaces, which was addressed as "dead-layer" phenomenon whose origin is still controversial. Here, both magnetic and structural properties of La 0.7 Sr0.3 MnO3/SrTiO3 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 La 0.7 Sr0.3 MnO3 and SrTiO3, as linked to the magnetism deterioration. Especially in La 0.7 Sr0.3 MnO3/SrTiO3 superlattices, the almost complete suppression of OOR in 4 unit-cell-thick La 0.7 Sr0.3 MnO3 results in a canted ferromagnetism. Detailed comparisons between strain and OOR relaxation and especially the observation of an unexpected La 0.7 Sr0.3 MnO3 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.