Pure ferromagnetism vs. re‐entrant spin glass behaviour in epitaxial La 0.7 Sr 0.3 MnO 3 on SrTiO 3 (001) and LaAlO 3 (001): the role of the substrate structural transition

Thin films of La 0.7 Sr 0.3 MnO 3 were grown by molecular beam epitaxy on ferroelastic SrTiO 3 (001) and LaAlO 3 (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 LaAlO 3 , while films on SrTiO 3 are untwinned. Low field dc magnetization measurements of films onto LaAlO 3 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 H 2/3 in the de Almeida–Thouless relation. Spin‐glass‐like features are absent in films on SrTiO 3 , 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. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)