J. Phys. D: Appl. Phys. 44, 345001 (2011)

M. Ziese, I. Vrejoiu, E. Pippel, A. Hähnel, E. Nikulina, and D. Hesse

Abstract

High-quality Pr_0.7Ca_0.3MnO₃/SrRuO₃ superlattices with ultrathin layers were fabricated by pulsed-laser deposition on SrTiO₃ substrates. The superlattices were studied by atomically resolved scanning transmission electron microscopy, high-resolution transmission electron microscopy, resistivity and magnetoresistance measurements. The superlattices grew coherently without growth defects. Viewed along the growth direction, SrRuO₃ and Pr_0.7Ca_0.3MnO₃ layers were terminated by RuO₂ and MnO₂, respectively, which imposes a unique structure to their interfaces. Superlattices with a constant thickness of the SrRuO₃ layers, but varying thickness of the Pr_0.7Ca_0.3MnO₃ layers showed a change of crystalline symmetry of the SrRuO₃ layers. At a low Pr_0.7Ca_0.3MnO₃ layer thickness of 1.5 nm transmission electron microscopy proved the SrRuO₃ layers to be orthorhombic, whereas these were non-orthorhombic for a Pr_0.7Ca_0.3MnO₃ layer thickness of 4.0 nm. Angular magnetoresistance measurements showed orthorhombic (with small monoclinic distortion) symmetry in the first case and tetragonal symmetry of the SrRuO₃ layers in the second case. Mechanisms driving this orthorhombic to tetragonal transition are briefly discussed.