Novel sol-gel processing for polycrystalline and epitaxial thin films of La0.67Ca0.33MnO3 with colossal magnetoresistance

A novel sol-gel processing method has been developed to fabricate homogeneous powder, polycrystalline and epitaxial thin film of La1-xCaxMnO3. Homogeneous powders of single phase La1-xCaxMnO3 were synthesized below 400 degrees C. Polycrystalline thin films were fabricated on Si(100) with a thermally oxidized SiO2 layer, while epitaxial films were grown on LaAlO3(100) and MgO(100) single crystal substrates. The films were composed of uniformly distributed spherical grains with diameters in the range of 100-1000 Angstrom, depending on annealing temperature. The surface rms roughnesses were 60-80 Angstrom. All films displayed a typical behavior of colossal magnetoresistive oxides: semiconductor-metal transitions accompanied by magnetic transitions were observed, and a peak MR ratio occurred near the transition temperatures. The peak MR ratio, (R-0 - R-H)/R-H, ranged from 30% to 90% at a field of H = 9000 Gauss, depending on the annealing temperature. The optimized MR performance was obtained in the thin films deposited on LaAlO3(100) and annealed at 900 degrees C in O-2. It is proposed that a higher MR ratio is associated with larger grains.