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ABSTRACT The strain inhomogeneity and crystallographic domain structures and their influence on the electrical transport and magnetic properties of epitaxial colossal magnetoresistive La,.xCaxMnO 3 (x = 0.2, 0.33) films have been studied as a function of film thickness and two types of (001) substrates, SrTiO 3 and LaAI03. 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 ( 0 0 1 )T and (1 10)T textures, and increased mosaic spread and surface roughness. The films also exhibit electrically insulating "dead" layers about 100 - 200A thick.

INTRODUCTION Doped manganite colossal magnetoresistance (CMR) materials exhibit mutual coupling among the spin, charge and lattice degrees of freedom that gives rise to many unique properties.[1],[2] Their electrical and magnetic properties, such as Curie temperature (T,), resistivity, and magnetoresistance, have been shown to be extremely sensitive to both chemical pressure stemming from alkaline-earth substitution of the rare-earth ions and hydrostatic pressure.[3]-[5] Recently, effects of strain on their properties have been probed extensively. For instance, the discovery of CMR effect in epitaxial thin films of doped LaMnO3 , has been attributed to the presence of lattice strain, since the observed behavior is not present in the corresponding bulk material. Furthermore, Jin et al. have shown that the CMR effect in epitaxial Lal.xCaxMnO 3 (LCMO) films decreases with increasing film thickness, and they have attributed the finding to strain relaxation.[6] More recently, several groups have shown that strain also plays a dominant role in magnetic anisotropy of LCMO and Lao7 Sr 0.3MnO 3 (LSMO) films.[7]-[10] Millis et al. have studied the effects of strain in LCMO films by measuring the out-of-plane lattice parameters and combining them with in-plane strains from calculations using Poisson's ratio, and by assuming coherence in the growth plane for films thinner than 150A.[l 1],[12] Aarts et al. have reported the effect of structural disorder on the magnetization and transport properties of epitaxial LCMO thin films by studying the thickness dependent structural changes.[13] In order to study the structural dependence of magnetic and electrical transport properties of these films, it is essential to character