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 charac terized by colossal negative magnetoresistance. Ultrathin, wedge-type films (0-120 Angstrom) of La0.7Ba0.3MnO3 were deposited by laser ablation onto S rTiO3 and LaAlO3 substrates. The films were patterned into strips of differ ent thickness and magneto-transport measurements were performed at temperat ures between 5 and 290 K and in magnetic fields up to 5 T. Atomic force- an d transmission electron microscopy were done to correlate the microstructur e with the transport data. The resistivity of the films increases slightly with decreasing thickness due to substrate-induced compressive strain. Belo w 50 Angstrom, the resistivity rises abruptly indicating a crossover to dis continuous and finally island-like film growth as confirmed by the microstr uctural techniques. At thicknesses slightly above the threshold for percola tive conduction (approximate to 30 Angstrom), an enhanced low-field magneto resistance was observed as a signature of spin-dependent tunneling. (C) 200 1 American Institute of Physics.