Effects of film thickness and lattice mismatch on strain states and magnetic properties of La0.8Ca0.2MnO3 thin films

The effects of strain relaxation on the crystallographic domain structure a nd on the magnetic and transport properties of epitaxial colossal magnetore sistive La0.8Ca0.2MnO3 (LCMO) thin films have been studied. LCMO films in t he thickness range of 100-4000 Angstrom were grown on (001) SrTiO3 and (001 ) LaAlO3 substrates, which impose an in-plane tensile and an in-plane compr essive biaxial stress in the films, respectively. On (001) SrTiO3 substrate s, the films can be grown coherently up to a thickness similar to 250 Angst rom, then strain relaxation occurs at a thickness of similar to 500 Angstro m. In contrast, even the 100 Angstrom film grown on (001) LaAlO3 is partial ly relaxed, and the critical thickness for complete strain relaxation is si milar to 750 Angstrom. The very thin films (<250 Angstrom) show a pure (001 )(T) normal orientation for growth on SrTiO3 and a pure (110)(T) texture fo r growth on LaAlO3. As thickness increases, the lattice strain relaxes, res ulting in mixed (001)(T) and (110)(T) textures for growth on both substrate s. Both the Curie and peak resistivity temperatures increase with increasin g film thickness, but they do not exhibit a correlation to strain states of the film. (C) 1999 American Institute of Physics. [S0021-8979(99)35008-8].