Flux pinning properties of YBCO/DyBCO multilayers

Multilayered structures of YBa(2)CU(3)O(7-delta) (YBCO) interlayered with thin layers of DyBa(2)Cu(3)O(7-delta) (DyBCO) were prepared on CeO(2)-buffered r-cut sapphire (Al(2)O(3)) substrates by pulsed laser deposition. Evaluation of the magnetic-field angular dependence of the critical current density [J(c)(H, theta)] 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 multilayers are highly anisotropic, i.e., the angular-dependent J(c) exhibits a very prominent peak when the applied magnetic field (H) is oriented parallel to the ab-plane direction (H parallel to ab). Analysis of the J(c)(H, theta) data revealed an enhanced random pinning for the multilayers for the entire range of field investigated. In the angular-dependent J, data, correlated pinning along the c-axis crystallographic direction was also evidenced at low applied fields by a less prominent peak at H parallel to 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 J(c)(H parallel to ab) to J(c)H parallel to c) is significantly enhanced. In addition to enhanced random pinning, it is considered that improved pinning along the H parallel to ab direction occurs due to ab-correlated pinning, arising from intrinsic pinning and possibly extended planar defects. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2978351]