CMR films structure as a function of growth and processing

Among the family encompassed by the complex metal oxides are the colossal magneto-resistive perovskites with potential applications in advanced high density magnetic data storage and sensor devices based on single or multilayers of these materials fabricated by vapor phase deposition methods. Realization of this potential requires solving basic thin film fabrication problems coupled to understanding the resulting structure-properties relationships. The specific objectives addressed in this study were to determine the dependence of growth and transport properties: (1) reproducibility on the pulsed laser deposition (PLD) target, (2) on sputter deposition chamber gas and substrate, and (3) on a post-deposition anneal in a reducing atmosphere. Toward these ends, we have grown La_0.67Ca_0.33MnO₃ films on perovskite substrates by PLD and RF off-axis sputter deposition from stoichiometric targets at temperatures from 400 to 900°C. The PLD films were grown from a new commercial target and post-deposition annealed in O₂ to reproduce, for comparison, the conditions used previously for the films grown with an in-house fabricated target. The sputter deposited films were grown in both Ar-O₂ mixed and Ar-only atmospheres, some grown simultaneously on different substrates; one Ar-O₂ grown film was post-annealed in a reducing atmosphere. Microstructures were studied by scanning probe microscopies and temperature-dependent transport properties by 4-point resistance measurements. Previously we reported on characterization of the T_substrate(T_s)-dependent microstructure of PLD as-deposited and post-annealed films grown from an in-house fabricated target. Annealed films grown from the new commercial target exhibited improved consistency in T-dependent transport and magnetization properties, independent of growth temperature. None of the as-grown sputter deposited films grown in the Ar-O₂ mixture exhibited a metallic transition while those grown in Ar-only at T_s > 800°C had a range of transition temperatures between 110 and 180 K. The variation in substrate-dependent structure demonstrated again the sensitivity of growth mechanism to template. Finally, the 500°C film grown in the Ar-O₂ mixture, went from insulating at all T's to exhibiting a 215°C metallic transition after the reducing anneal treatment.