Study of phenomena induced by interfacial oxygen octahedra coupling in La_0.5Sr_0.5CoO_3-δ/SrTiO₃ heterostructures using Cryo-STEM

In recent years epitaxial transition metal oxide thin films with broken symmetry have been studied extensively due to their novel magnetization and transport properties. Ferromagnetic La_0.5Sr_0.5CoO_3-δ (LSCO) thin films grown on SrTiO₃ exhibit oxygen vacancy ordering which is absent in bulk, while SrTiO₃ undergoes antiferrodistortive phase transition at 105 K being triggered by rotations of the TiO₆ octahedra. This structural symmetry breaking accommodated by interfacial lattice mismatch modifies the Ti-O-Co bond angle at the interface, and hence distorts both CoO₆ octahedral and CoO₄ tetrahedral structures in LSCO thin films. Here, we use aberration-corrected scanning transmission electron microscopy combined with an in situ TEM cryo-holder to compare the atomic/electronic structure and magnetic properties of La_0.5Sr_0.5CoO_3-δ thin films grown on SrTiO₃, below and above 105 K. Atomic-resolution imaging and electron energy-loss spectroscopy (EELS) are used to examine variations in the local density of states and magnetic moments as a function of sample temperature.