Lattice-mismatch-strain induced inhomogeneities in epitaxial La0.7Ca0.3MnO3 films

Epitaxial La0.7Ca0.3MnO3 (LCMO) films of 15-150 nm thick have been grown on SrTiO3(001) [STO(001)] and (LaAlO3)(0.3)(Sr2AlTaO6)(0.7)(001) [LSAT(001)] substrates with lattice mismatches of 1.11% and 0.15%, respectively. Asymmetric x-ray reciprocal space mapping was used to determine the strain state evolution in the films. For LCMO/STO(001), as the film thickness increases, at about 30 nm a change from fully to partially strained has been induced, and a further annealing at 900 degrees C can fully relax the films. For LCMO/LSAT(001), however, due to the negligible lattice mismatch, even at 15 nm the films are almost fully relaxed. Correspondingly, for the fully relaxed LCMO films a paramagnetic to ferromagnetic transition at T-C of about 260 K was observed, and for those partially relaxed, both the structure and magnetic transition are inhomogeneous, two thickness-dependent T-C were detected for each film. The results show strong evidence that the transition temperature is correlated with the strain state in epitaxial LCMO films. (c) 2007 American Institute of Physics.