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 and on the magnetic and transport properties of epitaxial colossal magnetoresistive La0.8Ca0.2MnO3 (LCMO) thin films have been studied. LCMO films in the 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 compressive biaxial stress in the films, respectively. On (001) SrTiO3 substrates, the films can be grown coherently up to a thickness similar to 250 Angstrom, then strain relaxation occurs at a thickness of similar to 500 Angstrom. In contrast, even the 100 Angstrom film grown on (001) LaAlO3 is partially relaxed, and the critical thickness for complete strain relaxation is similar 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 for growth on LaAlO3. As thickness increases, the lattice strain relaxes, resulting in mixed (001)(T) and (110)(T) textures for growth on both substrates. Both the Curie and peak resistivity temperatures increase with increasing 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].