Thickness dependence of microstructure in thin La_0.7Sr_0.3MnO₃ films grown on (1 0 0) SrTiO₃ substrate

This study investigates the nanostructure of perovskite thin films, and its influence on magnetic properties. Epitaxial thin films of perovskite ${La}_{0.7}$ ${Sr}_{0.3}$MnO₃ with thickness ranging from $13.5$ nm to 320 nm were deposited on SrTiO₃ (1 0 0) substrates using pulsed laser deposition techniques. X-ray diffraction, along with high-resolution transmission electron microscopy (HRTEM) investigations were carried out, and showed the presence of a second, La-rich phase in thick film. Scanning electron microscopy analysis showed thinner films to have smooth surfaces, while thicker films presented large triangular shapes emerging out of the film surface. Also HRTEM images revealed epitaxial growth for thinner films. Thicker films grow with numerous misfit dislocations leading to columnar structure, where the thickest film presents branched structure with an intermediate La-rich layer. Lattice mismatch, diffusion of Mn ions into the substrate and substituting Ti ions are known as sources of strain in films near interfaces. Magnetic properties in the structure mentioned are described by double-exchange interaction, which is very sensitive to local structure. Hence, the nanostructure of films reported here has a remarkable effect on their magnetic properties. (paper)