Three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive La0.8Ca0.2MnO3 thin films

The evolution of three-dimensional strain states and crystallographic domain structures of epitaxial colossal magnetoresistive ${\mathrm{La}}_{\mathrm{0.8}}{\mathrm{Ca}}_{\mathrm{0.2}}{\mathrm{MnO}}_{\mathrm{3}}$ films have been studied as a function of film thickness and lattice mismatch with two types of (001) substrates, ${\mathrm{SrTiO}}_{\mathrm{3}}$ and ${\mathrm{LaAlO}}_{\mathrm{3}}.$ In-plane and out-of-plane lattice parameters and strain states of the films were measured directly using normal and grazing incidence x-ray diffraction techniques. The unit cell volume of the films is not conserved, and it exhibits a substrate-dependent variation with film thickness. Films grown on ${\mathrm{SrTiO}}_{\mathrm{3}}$ substrates with thickness up to ∼250 Å are strained coherently with a pure ${\text{(001)}}^T$ orientation normal to the surface. In contrast, films as thin as 100 Å grown on ${\mathrm{LaAlO}}_{\mathrm{3}}$ show partial relaxation with a ${\text{(110)}}^T$ texture. While thinner films have smoother surfaces and higher crystalline quality, strain relaxation in thicker films leads to mixed ${\text{(001)}}^T$ and ${\text{(110)}}^T$ textures, mosaic spread, and surface roughening. The magnetic and electrical transport properties, particularly Curie and peak resistivity temperatures, also show systematic variations with respect to film thickness.