3-DIMENSIONAL STRAIN STATES AND CRYSTALLOGRAPHIC DOMAIN-STRUCTURES OFEPITAXIAL COLOSSAL MAGNETORESISTIVE LA0.8CA0.2MNO3 THIN-FILMS

The evolution of three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive La0.8Ca0.2MnO 3 films have been studied as a function of film thickness and lattice mismatch with two types of (001) substrates, SrTiO3 and LaAlO3. In-pla ne and out- of- plane lattice parameters and strain states of the film s were measured directly using normal and grazing incidence x-ray diff raction techniques. The unit cell volume of the films is not conserved , and it exhibits a substrate-dependent variation with film thickness. Films grown on SrTiO3 substrates with thickness up to similar to 250 Angstrom are strained coherently with a pure (001)(T) orientation norm al to the surface. In contrast, films as thin as 100 Angstrom grown on LaAlO3 show partial relaxation with a (110)(T) texture. While thinner films have smoother surfaces and higher crystalline quality, strain r elaxation in thicker films leads to mixed (001)(T) and (110)(T) textur es, mosaic spread, and surface roughening. The magnetic and electrical transport properties, particularly Curie and peak resistivity tempera tures, also show systematic variations with respect to film thickness. (C) 1998 American Institute of Physics. [S0003-6951(98)02848-4].