Magnetoresistance behavior in external, internal and mixed doped lanthanum manganite thin films

A systematic investigation focused on the magnetoresistance behavior of La0.7Ca0.3MnO3, La0.7,MnO3 and La0.7Ca0.2MnO3 thin films has been carried out. Thin films of these materials have been grown in situ on (100) LaAlO3 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. As indicated by their unit chemical formulae, these films represent external, internal and mixed (external and internal) doped lanthanum manganite systems, respectively. Electrical resistance and magnetoresistance have been measured in the 10-300 K range in magnetic field up to 5T using SQUID magnetometer. The MR ratios of La0.7Ca0.3MnO3, La0.7MnO3, and La0.7Ca0.2MnO3 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.