Substrate, annealing, and Mn excess effects on La-Ca-MnO3 thin films grownby metalorganic chemical vapor deposition: A way to room-temperature T-c

Oriented thin films of the La-Ca-MnO3 system with several Mn-excess composi tions were prepared by aerosol-assisted metalorganic chemical vapor deposit ion. Depositions both on MgO (100) and LaAlO3 (100) substrates were perform ed at temperatures between 700 and 800 degrees C, with 30 min in situ oxyge n annealing at the deposition temperature. The films deposited on LaAlO3 ha ve much better structural quality with rocking curves of 0.3-0.7 full width at half maximum and higher T-c. For films with Mn excess, an ex situ annea ling (800 degrees C for 1 h in flowing oxygen) increases T-c dramatically, from 180-190 K to values in the range 240-296 K, above the maximum T-c of t he stoichiometric, optimally doped La0.67Ca0.33MnO3 composition. This behav ior may be associated with the presence of La vacancies, which act as self- dopants, and whose role is enhanced after suitable annealing. The films pre sent high magnetoresistance values in the vicinity of the critical temperat ures: at 7 kOe, 32% for a film with T-c = 279 K and 13% for a film with T-c = 296 K. The magnetic properties of the films on MgO were degraded by anne aling, probably due to Mg diffusion to the film. (C) 1999 American Institut e of Physics. [S0021-8979(99)49708-7].