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 La0.7Sr0.3MnO3 is strongly modified near interfaces, which was addressed as “dead-layer” phenomenon whose origin is still controversial. Here, both magnetic and structural properties of La0.7Sr0.3MnO3/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 La0.7Sr0.3MnO3 and SrTiO3, as linked to the magnetism deterioration. Especially in La0.7Sr0.3MnO3/SrTiO3 superlattices, the almost complete suppression of OOR in 4 unit-cell-thick La0.7Sr0.3MnO3 results in a canted ferromagnetism. Detailed comparisons between strain and OOR relaxation and especially the observation of an unexpected La0.7Sr0.3MnO3 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.
Highlights
Proposed[22,23]; interfacial orbital reconstruction might occur destroying the double-exchange interaction close to the interface[24,25,26]; there might be interfacial charge transfer[18,27,28,29]
An oxygen octahedral rotation (OOR) mismatch of ~10° across the LSMO/STO hetero-interface leads to a significant alteration of the rotation angles in both STO and LSMO layers, such that the suppression of OOR in LSMO can be intuitively linked to the deterioration of magnetism
Two representative samples were selected: (1) a triple layer sandwich-like sample consisted of two LSMO layers with thicknesses of 10 and 20 u.c. spaced by a 3 u.c. thick STO interlayer; (2) a LSMO/STO superlattice consisting of 15 bilayers of 4 u.c. thick LSMO and 6 u.c. thick STO
Summary
Proposed[22,23]; interfacial orbital reconstruction might occur destroying the double-exchange interaction close to the interface[24,25,26]; there might be interfacial charge transfer[18,27,28,29]. In LSMO/STO based heterostructures, both LSMO and STO have ABO3 type perovskite structure, but due to different tolerance factors, STO is cubic at room temperature with a transition to a tetragonal phase below 105 K, whereas LSMO is rhombohedral in bulk[31], but orthorhombic/tetragonal in thin films[32,33] This demonstrates that the perovskite structure is versatile in accommodating chemical strain, as well as external structural strain. The almost complete suppression of OOR in 4 u.c. thick LSMO within a LSMO/STO superlattice results in a strongly canted magnetism, which discloses the previously reported magnetic-dead-layer phenomenon These findings suggest an efficient interfacial engineering mechanism of magnetic and electronic properties through OOR coupling at the atomic scale
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