Substrate, annealing, and Mn excess effects on La–Ca–MnO3 thin films grown by metalorganic chemical vapor deposition: A way to room-temperature Tc

Abstract

Oriented thin films of the La–Ca–MnO3 system with several Mn-excess compositions were prepared by aerosol-assisted metalorganic chemical vapor deposition. Depositions both on MgO (100) and LaAlO3 (100) substrates were performed at temperatures between 700 and 800 °C, with 30 min in situ oxygen annealing at the deposition temperature. The films deposited on LaAlO3 have much better structural quality with rocking curves of 0.3–0.7 full width at half maximum and higher Tc. For films with Mn excess, an ex situ annealing (800 °C for 1 h in flowing oxygen) increases Tc dramatically, from 180–190 K to values in the range 240–296 K, above the maximum Tc of the stoichiometric, optimally doped La0.67Ca0.33MnO3 composition. This behavior may be associated with the presence of La vacancies, which act as self-dopants, and whose role is enhanced after suitable annealing. The films present high magnetoresistance values in the vicinity of the critical temperatures: at 7 kOe, 32% for a film with Tc=279 K and 13% for a film with Tc=296 K. The magnetic properties of the films on MgO were degraded by annealing, probably due to Mg diffusion to the film.