Abstract
The results of preparation and post-treatment conditions on the long-term stability of Co-substituted nanostructured manganite La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.81</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.19</sub> Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.09</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.06</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films are presented. The films were grown on polycrystalline Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrates by pulsed-injection metal-organic chemical vapor deposition technique at 600 °C keeping different growth rates (9, 13, and 27 nm/min), thus inducing different levels of disorder in the films. For comparison, the reference epitaxial films were deposited on the LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> substrate. The changes of resistivity and magnetoresistance (MR; up to 20 T) during the long-term storage of the films and accelerated aging by annealing the films in O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> or Ar atmosphere at ~100 °C were studied. It was found that the annealing atmosphere and long-term storage have a significant influence on the film resistivity and metal–insulator transition temperature, while MR magnitude is affected insignificantly. The aging 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.
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