Vortex pinning properties at dc and microwave frequencies of YBa <sub>2</sub> Cu <sub>3</sub> O <sub>7-x</sub> films with nanorods and nanoparticles
Elena Bartolomé, Jordi Alcalà, Ferrán Vallés, Teresa Puig, X. Obradors, Nicola Pompeo, Andrea Alimenti, Kostiantyn Torokhtii, F. Rizzo, A. Augieri, G. Celentano, Enrico Silva, Anna Palau
Abstract
Abstract YBa 2 Cu 3 O 7−x (YBCO) nanocomposites for wire applications need to operate in a broad range of frequencies, ranging from dc in magnets to GHz in cavities and screenings of future particle accelerators. We have investigated the in-field and angular vortex pinning performance in dc and at 50 GHz of two types of nanocomposites, pulsed laser deposition (PLD) YBCO with mixed Ba 2 YNbO 6 + Ba 2 YTaO 6 (BYNTO) nanorods and chemical solution deposited (CSD) YBCO with BaHfO 3 (BHO) nanoparticles (NPs), and the pristine counterpart films, grown on top of single-crystalline substrates. Transport measurements performed up to 9 T between 5 and 77 K show that CSD nanocomposites exhibit a smooth field decay and increased single-to-collective crossover field H * compared to pristine samples, associated to the enhanced isotropic pinning contribution induced by the NPs, while PLD films exhibit unchanged H * and superior critical current densities up to higher irreversibility fields, associated to the anisotropic contribution introduced by the rods. Microwave in-field measurements of the pinning constant k p revealed CSD NCs exhibit a qualitatively similar, but smoother k p ( H ) than pristine samples, whereas for PLD samples, a growing k p ( H ) dependence is observed as a result of the increased relevance of the stiffness of the fluxons pinned by nanorods.