Phase transitions: an alternative for stress accommodation in CMR manganate films

Abstract

Thin films of perovskite-based material, exhibiting colossal magnetoresistance properties have been structurally characterized. The lattice mismatch with the substrate and the associated stress can induce different types of distortions in the film, resulting in different crystal structures. This opens the possibility to design new structures with predictable physical properties. The structure of epitaxial La 0.1 Sr 0.9 MnO 3 on a (100) SrTiO 3 substrate and of the epitaxial composite (La 0.67 Ca 0.33 MnO 3 ) 1-x : (MgO) x films on a (100)MgO substrate have been investigated by electron microscopy. Novel mechanisms for misfit accommodation in epitaxial films have been detected. For the La 0.1 Sr 0.9 MnO 3 /(100)SrTiO 3 film, where there is only a small mismatch (a F a S ), the formation of periodic micro-twins is observed. For the composite (La 0.67 Ca 0.33 MnO 3 ) 1-x : (MgO) x /(100)MgO films under a 3D stress (mismatch 8 %), a phase transition from low to high symmetry is detected.