Homogeneous strain-relaxation effects in La_0.67Ca_0.33MnO₃ films grown on NdGaO₃

X-ray diffraction and transport measurements on a series of La_0.67Ca_0.33MnO₃ films grown on (110)-cut NdGaO₃ substrates are presented. Contrary to widespread belief assuming strain-free growth, this work shows the presence of strain in a 42 nm film. On increasing thickness structural relaxation occurs, reaching a bulklike state for 500 nm. No evidence of coexistence of strained and relaxed regions is found. The evolution of lattice parameters toward bulk values is accompanied by an increase of the metal-to-insulator transition temperature and a decrease of the polaron activation energy. Therefore, strain effects cannot always be neglected in La_0.67Ca_0.33MnO₃ films grown on small-mismatch NdGaO₃.