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La0.625Ca0.375MnO3 (LCMO) films with thicknesses between 7 and 54 nm were epitaxially grown on (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) [LSAT (001)] substrates by using pulsed laser deposition. For this epitaxial system, antiferromagnetic-insulator (AFI) state can be controlled by changing the film thickness and annealing time with various epitaxial strain states, although this phenomenon is absent in the relatively thick films or bulk samples. The consistency between magnetization and resistivity data suggests all these interesting transport behaviors are attributed to the fluctuation of AFI volume fractions and their instability. Especially, there are huge low-field magnetoresistance over -54% (32 nm) at 0.1 T and enhanced magnetoresistance over a broad temperature range. Based on these above results, annealing induced coherent evolutions of biaxial strain and AFI phase in LCMO epitaxial films is a consequence of the strain-driven orbital ordered state, and this may make an approach for a possible application of strongly correlated electron devices. [ABSTRACT FROM AUTHOR]

La0.625Ca0.375MnO3 films have been epitaxially grown on the (LaAlO3)0.3(Sr2AlTaO6)0.35 (001) substrates at different oxygen pressures and show varying tetragonal distortion. Results indicate a tendency that larger tetragonal distortion can stabilize the antiferromagnetic-insulator phase in the thin films. Colossal magnetoresistance (CMR) and anisotropic magnetoresistance (AMR) have been greatly enhanced only in the strained films over a broad temperature, probably responding to the anisotropic fluctuation of the nanoscale orientation-ordered patterns near the temperature of the phase separation region or metal-insulator transition. Hence, the inhomogeneous phase competition may contribute to the CMR and the extraordinary AMR effect for manganite devices. [ABSTRACT FROM AUTHOR]