Influence of preparation conditions on long-term stability of magnetoresistive properties of nanostructured La-Sr-Mn-Co-O films grown by PI MOCVD

Abstract

The results of preparation and post-treatment conditions on long-term stability of Co-substituted nanostructured manganite La0.81Sr0.19Mn1.09Co0.06O3 films are presented. The films were grown on polycrystalline Al2O3 substrates by Pulsed-Injection Metal-Organic Chemical Vapor Deposition technique at 600 °C keeping different growth rates (9 nm/min, 13 nm/min, and 27 nm/min) thus inducing different level of disorder in the films. For comparison, the reference epitaxial films were deposited on LaAlO3 substrate. The changes of resistivity and magnetoresistance (up to 20 T) during the long-term storage of the films and accelerated ageing by annealing the films in O2 or Ar atmosphere at ~100 °C were studied. It was found, that the annealing atmosphere and long-term storage has significant influence on the film resistivity and metal-insulator transition temperature, while magnetoresistance magnitude is affected insignificantly. The ageing effects have the highest influence on the nanostructured film grown at the highest growth rate, while for epitaxial films the changes are negligible. The observed changes were analyzed using Mott&s variable range hopping model and explained by oxygen depletion and diffusion in grain boundaries of nanostructured films. The ways to stabilize the main parameters of the manganite-cobaltite films for the development of high magnetic field sensors are discussed.