MAGNETORESISTANCE BEHAVIOR IN LA0.7CAXMNO3 (X = 0, 0.2, AND 0.3) THIN-FILMS

A systematic investigation focused on the magnetoresistance (MR) behav ior of La0.7CaxMnO3 (x=0, 0.2, and 0.3) thin films has been carried ou r. As indicated by the unit chemical formula, La0.7CaxMnO3 films with x = 0.3, 0, and 0.2 represent external, internal, and mixed (external and internal) doped lanthanum manganite systems, respectively. Thin fi lms of these materials have been grown in situ on (100) LaAlO3 substra tes using a pulsed laser deposition technique. Microstructural charact erization carried out on these films has shown that the films are smoo th, free from impurities, and highly textured. Electrical resistance a nd magnetoresistance have been measured in the 10-300 K range in magne tic held up to 5 T using a superconducting quantum interference device magnetometer. The MR ratios of La0.7Ca0.3MnO3 (x=0.3), La0.7MnO3 (x=0 ), and La0.7Ca0.2MnO3 (x=0.2) films are found to be 825%, 700%, and 75 0% at 200 K, 240 K, and 220 K, respectively. The variation in the insu lator to metal transition and the MR ratio is attributed to internal c hemical pressure and vacancy localization effects.