Growth andc-axis flux pinning of nanostructured YBCO/BZO multilayers

A systematic investigation of superconducting multilayered films composed of alternating nanostructured YBa2Cu3O6+x (YBCO) and secondary phase BaZrO3 (BZO) layers is carried out. Detailed growth mechanism studies of these structures as well as superconducting properties in a wide temperature and magnetic field range are investigated by varying the thicknesses of layers grown by pulsed laser deposition. Structural analysis shows that multilayering changes clearly the growth mechanism of YBCO. Alternating thin BZO layers smoothen the film surface, create in-plane mosaic spread structure of the YBCO crystals, produce stress in the BZO interface region and moreover improve the out-of-plane alignment of YBCO. Magnetic measurements of superconducting properties demonstrate that the critical temperature decreases slightly when the thickness of the BZO layers increases relative to the YBCO layers. This indicates a growing strain effect at the layer interfaces. At the same time, critical current densities of multilayers in the whole used temperature and magnetic field range are increased to the same level as in conventionally BZO-doped YBCO films when very thin alternating YBCO/BZO layer structures are deposited. This thickness dependent result is explained by the dense flux pinning centre network in layered superconductors, giving the opportunity to increase the overall thickness of a film and further enhance the current-carrying capability.