Structural and magnetic properties of ultrathin epitaxial La0.7Ca0.3MnO3 manganite films:: Strain versus finite size effects

We present a structural and magnetic study of La0.7Ca0.3MnO3 epitaxial films (the thickness ranges from 2.4 to 80 nm) on SrTiO3. Their structure, as obtained by x-ray diffraction, is orthorhombic with a 45degrees rotated 2x2 square lattice, referred to the SrTiO3 substrate, in the film plane. The 2.4 nm film adopts a different structure as evidenced by the extinction of particular diffraction peaks and supported by the behavior of the size of the in-plane structural domains. While no important structural changes are detected for the other films as the layer thickness is reduced, T-c decreases drastically while the remanent magnetization is constant. T-c follows the functional dependence of a mean field approximation for the limitation of the divergence of the spin-spin correlations by the film thickness. (C) 2003 American Institute of Physics.