Influence of the morphology on the magneto-transport properties of laser-ablated ultrathin La0.7Ba0.3MnO3 films

We investigate the thickness dependent properties of manganite films characterized by colossal negative magnetoresistance. Ultrathin, wedge-type films (0–120 A) of La0.7Ba0.3MnO3 were deposited by laser ablation onto SrTiO3 and LaAlO3 substrates. The films were patterned into strips of different thickness and magneto-transport measurements were performed at temperatures between 5 and 290 K and in magnetic fields up to 5 T. Atomic force- and transmission electron microscopy were done to correlate the microstructure with the transport data. The resistivity of the films increases slightly with decreasing thickness due to substrate-induced compressive strain. Below 50 A, the resistivity rises abruptly indicating a crossover to discontinuous and finally island-like film growth as confirmed by the microstructural techniques. At thicknesses slightly above the threshold for percolative conduction (≈30 A), an enhanced low-field magnetoresistance was observed as a signature of spin-dependent tunneling.