Unit-cell thick BaTiO3 blocks octahedral tilt propagation across oxide heterointerface

Abstract

We fabricated SrRuO3/BaTiO3/GdScO3 heterostructures in which the BaTiO3 layer is one unit cell thick by pulsed laser deposition and elucidated how the BaTiO3 layer influences structural and magneto-transport properties of the SrRuO3 layer through octahedral connections across the heterointerface. Our X-ray-diffraction-based structural characterizations show that while an epitaxial SrRuO3 layer grown directly on a GdScO3 substrate is in the monoclinic phase with RuO6 octahedral tilts, a one-unit-cell-thick BaTiO3 layer inserted between SrRuO3 and GdScO3 stabilizes the tetragonal SrRuO3 layer with largely reduced RuO6 tilts. Our high-angle annular dark-field and annular bright-field scanning transmission electron microscopy observations provide an atomic-level view of the octahedral connections across the heterostructure and reveal that the BaTiO3 layer only one unit cell thick is thick enough to stabilize the RuO6-TiO6 octahedral connections with negligible in-plane oxygen atomic displacements. This results in no octahedral tilts propagating into the SrRuO3 layer and leads to the formation of a tetragonal SrRuO3 layer. The magneto-transport property characterizations also reveal a strong impact of the octahedral connections modified by the inserted BaTiO3 layer on the spin-orbit interaction of the SrRuO3 layer. The SrRuO3 layer on BaTiO3/ GdScO3 has in-plane magnetic anisotropy. This is in contrast to the magnetic anisotropy of the monoclinic SrRuO3 films on the GdScO3 substrate, in which the easy axis is ∼45° to the film surface normal. Our results demonstrate that the one-unit-cell-thick layer of BaTiO3 can control and manipulate the interfacial octahedral connection closely linked to the structure-property relationship of heterostructures.