Transport parameters of granular La0.67Ca0.33MnO3 films grown on an R-Plane sapphire

Precisely (100)-oriented, 200-nm thick La0.67Ca0.33MnO3 films have been grown by laser ablation on a sapphire (R-plane) substrate covered by a (100)SrTiO3/(001)Bi2SrNb2O9/(001)CeO2 trilayer buffer. The azimuthal misorientation of crystal grains (50-300 nm) in the La0.67Ca0.33MnO3 films decreased by about 40% as the condensation temperature was increased ered from 760 to 810 degreesC. The lattice parameter of the grown manganate films was reduced to 3.81-3.82 A by enriching them with oxygen. The maximum in the temperature dependence of the electrical resistivity of the La0.67Ca0.33MnO3 films grown was shifted toward lower temperatures by 20-50 K relative to its position for bulk ceramic samples of a stoichiometric composition. The largest magnetoresistance (MR = 42% at H = 0.4 T) was found in La0.67Ca0.33MnO3 films with a Mn4+ concentration on the order of 50% (T = 166 K). (C) 2000 MAIK "Nauka/Interperiodica".