Influence of strain and annealing on microstructure and magnetic/electric properties of epitaxial (001) La0.70Ba0.30MnO3 films

This work is a transmission electron microscopy characterisation of one as grown and one annealed epitaxial (001) La0.70Ba0.30MnO3 (LBMO) single layer film, together with an as grown (001) SrTiO3/La0.70Ba0.30MnO3/SrTiO3 triple layer. All films had been pulsed laser deposited on (110)r LaAlO3 (LAO) substrates. The as grown single layer film had a columnar subgrain morphology and a residual in-plane compressive strain. Annealing or use of a SrTiO3 buffer layer resulted in a lower strain, where the buffer layer had the superior relaxation effect. It also decreased the subgrain boundary number density, resulting in an enhanced single crystal quality of the LBMO. Mn3O4 precipitates were present in all films and they nucleated at misfit dislocations or substrate surface irregularities. All LBMO films were 19-22% Mn-deficient, which may be a result from the presence of Mn3O4. The single layer films had an extra large (001) lattice parameter, which was due to 6-10% excess of La. Chemical analysis showed that even the as grown films had a high O-content, which in turn was reflected in the magnetic/electric behaviour. The low-angle grain boundaries had no effect on the properties. The as grown single layer film had a magnetic anisotropy in the [001] direction, but strain relaxation after annealing or lower initial strain in the buffered film resulted in a more homogeneous magnetisation.