Magnetic and structural phase transitions in epitaxial thin films of Manganites*

Understanding the magnetic properties of complex materials near interfaces is important for the development of functional nanostructures and devices. Epitaxial LaMnO$_{3}$ films were grown on SrTiO$_{3}$ substrates. Recent work on such thin-film samples has shown that ``interface doping'' can induce magnetism at interfaces. Our work on LaMnO$_{3}$/SrTiO$_{3}$ interfaces has shown that the nature of the interface determines its magnetic structure - with the MnO$_{2}$-SrO interface showing a different magnetization than the LaO-TiO$_{2}$ interface. To investigate interfacial structures, we used polarized neutron reflectometry with off-specular scattering. Our results give evidence of reversible temperature- and field- dependent structural changes in LaMnO$_{3}$ film which undergo a phase transition. We determined that a structural phase transition in SrTiO$_{3}$ and the misfit strain trigger appearance of twins to reduce stresses and to adjust lattice mismatch between the film and the substrate. We show that a laterally correlated superstructure appear due to interaction of structural modifications with the magnetization the film