Orthorhombic-to-tetragonal transition of SrRuO3 layers in Pr0.7Ca0.3MnO3/SrRuO3 superlattices
Résumé
High-quality Pr 0.7 Ca 0.3 MnO 3 /SrRuO 3 superlattices with ultrathin layers were fabricated by pulsed laser deposition on SrTiO 3 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, SrRuO 3 and Pr 0.7 Ca 0.3 MnO 3 layers were terminated by RuO 2 and MnO 2, respectively, which imposes a unique structure to their interfaces. Superlattices with a constant thickness of the SrRuO 3 layers, but varying thickness of the Pr 0.7 Ca 0.3 MnO 3 layers showed a change of crystalline symmetry of the SrRuO 3 layers. At a low Pr 0.7 Ca 0.3 MnO 3 layer thickness of 1.5 nm transmission electron microscopy proved the SrRuO 3 layers to be orthorhombic, whereas these were non-orthorhombic for a Pr 0.7 Ca 0.3 MnO 3 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 SrRuO 3 layers in the second case. Mechanisms driving this orthorhombic to tetragonal transition are briefly discussed.
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