Pure ferromagnetism vs. re-entrant spin glass behaviour in epitaxial La0.7Sr0.3MnO3 on SrTiO3(001) and LaAlO3(001): the role of the substrate structural transition

Thin films of La0.7Sr0.3MnO3 were grown by molecular beam epitaxy on ferroelastic SrTiO3(001) and LaAlO3(001) substrates, with ferroelastic transition at 105 K and 813 K respectively. High resolution X-ray diffraction analysis proves the presence of twins at room temperature in the films grown onto LaAlO3, while films on SrTiO3 are untwinned. Low field dc magnetization measurements of films onto LaAlO3 are discussed in terms of coexisting ferromagnetic and spin disordered regions, connected to twin cores and twin boundaries respectively; the freezing temperature of the spin glass subsystem scales as H2/3 in the de Almeida–Thouless relation. Spin-glass-like features are absent in films on SrTiO3, in which the ferroelastic transition of the substrate is only marked by a small bump in the low field dc magnetization. The different magnetic behaviour depends on being the ferroelastic transition above or below the film Curie point.