Magnetic signature of symmetry reduction in epitaxial La_(0.67)Sr_(0.33)MnO_3 films

摘要

The magnetic properties of epitaxially grown La_(0.67)Sr_(0.33)MnO_3 perovskite thin films were investigated to elucidate an unexpected broken symmetry between orthogonal [100] and [010] inplane directions, resulting from the magnetostructural coupling between the film and the cubic SrTiO_3 (001) substrate. The films were synthesized by molecular beam epitaxy with either complete or zero A-site cation disorder. Magnetization measured in [100] and [010] directions shows differences that signal a reduction of the in-plane cubic symmetry only for T < 290 K. The magnetization asymmetry is more robust in the film with complete A-site disorder. These results are attributed to a dominant Mn~(3+) character at the film-substrate interface and an associated out-of-plane bonding character with hypothesized origins in both charge imbalance and strain effects.