Strain Inhomogeneity in Epitaxial Colossal Magnetoresistive La1-xCaxMnO3 Thin Films

Abstract

AbstractThe strain inhomogeneity and crystallographic domain structures and their influence on the electrical transport and magnetic properties of epitaxial colossal magnetoresistive La1-xCaxMnO3 (x = 0.2, 0.33) films have been studied as a function of film thickness and two types of (001) substrates, SrTiO3 and LaAlO3. Out-of-plane and in-plane lattice parameters were determined using normal and grazing incidence x-ray diffraction (GID), and least-squares fits of off-axis x-ray reflections. The lattice strain near the film surface as determined by GID appears to relax faster than that at the film interior as determined by the least-squares fit, indicating the presence of strain inhomogeneity in the films. The observed strain inhomogeneity appears to influence the magnetic and electrical transport properties. In particular the measured temperature dependent magnetization exhibits multiple transitions indicating a variation of Curie temperatures within the same sample. While the very thin films exhibit single out-of-plane domains, accompanied by a high crystalline coherence and smooth surfaces, strain relaxation in thicker films leads to mixed ( 001)T and (110)T textures, and increased mosaic spread and surface roughness. The films also exhibit electrically insulating “dead” layers about 100 – 200Å thick.