Charge ordering in Pr0.5Ca0.5MnO3 thin films:: A new form initiated by strain effects of LaAlO3 substrate

The growth of [101] epitaxial films of Pr0.5Ca0.5MnO3 on LaAlO3 substrates has been achieved. The structure, nanostructure, and magnetotransport properties are reported and compared to those of the bulk material. The electron diffraction study evidences, at RT, a monoclinic cell with a approximate to c approximate to 5.4 Angstrom, b approximate to 7.6 Angstrom, and beta approximate to 91 degrees. The monoclinic distortion is assumed to be due to strain effects. At 92 K, a system of extra reflections is observed which implies an incommensurate modulated structure. The component q of the modulation vector along a* ranges between 0.35 and 0.40. The lattice images show that the modulation is established throughout the whole film. The q value observed in the film is significantly lower than the one of the bulk material. This effect is correlated to strain effects of the substrate, limiting the cell distortion induced by charge ordering. An unusual insulating-ferromagnetic phase is observed with a critical temperature of 240 K, close to the T-CO. (C) 2000 American Institute of Physics. [S0021- 8979(00)08415-2].