Flux pinning properties of YBCO/DyBCO multilayers

Abstract

Multilayered structures of YBa2Cu3O7−δ (YBCO) interlayered with thin layers of DyBa2Cu3O7-δ (DyBCO) were prepared on CeO2-buffered r-cut sapphire (Al2O3) substrates by pulsed laser deposition. Evaluation of the magnetic-field angular dependence of the critical current density [Jc(H,θ)] revealed that the flux pinning properties of multilayered YBCO/DyBCO films were significantly enhanced in comparison to single-layer YBCO films (monolayers) prepared using the same experimental parameters. The YBCO/DyBCO multilayers are highly anisotropic, i.e., the angular-dependent Jc exhibits a very prominent peak when the applied magnetic field (H) is oriented parallel to the ab-plane direction (H∥ab). Analysis of the Jc(H,θ) data revealed an enhanced random pinning for the multilayers for the entire range of field investigated. In the angular-dependent Jc data, correlated pinning along the c-axis crystallographic direction was also evidenced at low applied fields by a less prominent peak at H∥c. This result was further corroborated by the presence of defect microstructures comprised of linear and planar defects which were considered as strong sources of c-axis-correlated pinning. However, for higher applied fields the contribution of c-axis-correlated pinning is highly diminished and the ratio of Jc(H∥ab) to Jc(H∥c) is significantly enhanced. In addition to enhanced random pinning, it is considered that improved pinning along the H∥ab direction occurs due to ab-correlated pinning, arising from intrinsic pinning and possibly extended planar defects.