Atomic structure and microstructure of very thin films of La_0.73Ca_0.27MnO₃ on SrTiO₃

Abstract

Very thin films (less than 20 nm) of La_0.73Ca_0.27MnO₃ on SrTiO₃ substrates exhibit properties quite different from the bulk; they are ferromagnetic insulators instead of ferromagnetic metals. Electron microscopy shows that such thin films are perfectly smooth, single phase and crystalline, as are thicker films but that they have a structure (imposed by the lattice matching with the substrate) which is different from that of the bulk or thick films (much greater than 20 nm). The main features of this structure are a Jahn—Teller distortion of the MnO₆ octahedra (not present in the bulk) and tilts of the MnO₆ octahedra (different from the bulk).