Effects of film thickness and lattice mismatch on strain states and magnetic properties of La_0.8Ca_0.2MnO₃ thin films

The effects of strain relaxation on the crystallographic domain structure and on the magnetic and transport properties of epitaxial colossal magnetoresistive La_0.8Ca_0.2MnO₃ (LCMO) thin films have been studied. LCMO films in the thickness range of 100–4000 Å 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 ∼250 Å, then strain relaxation occurs at a thickness of ∼500 Å. In contrast, even the 100 Å film grown on (001) LaAlO₃ is partially relaxed, and the critical thickness for complete strain relaxation is ∼750 Å. The very thin films (≪250 Å) 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. © 1999 American Institute of Physics.