Magnetoresistance behavior in 0.2, and 0.3) thin films

A systematic investigation focused on the magnetoresistance (MR) behavior of (Formula presented) ((Formula presented) 0.2, and 0.3) thin films has been carried out. As indicated by the unit chemical formula, (Formula presented) films with (Formula presented) 0, and 0.2 represent external, internal, and mixed (external and internal) doped lanthanum manganite systems, respectively. Thin films of these materials have been grown in situ on (100) (Formula presented) substrates using a pulsed laser deposition technique. Microstructural characterization carried out on these films has shown that the films are smooth, free from impurities, and highly textured. Electrical resistance and magnetoresistance have been measured in the 10-300 K range in magnetic field up to 5 T using a superconducting quantum interference device magnetometer. The MR ratios of (Formula presented) and (Formula presented) films are found to be 825%, 700%, and 750% at 200 K, 240 K, and 220 K, respectively. The variation in the insulator to metal transition and the MR ratio is attributed to internal chemical pressure and vacancy localization effects. © 1998 The American Physical Society.