Angular and field dependent flux pinning in artificially doped YBCO films on IBAD-MgO based template

Abstract

The self-organized artificial pinning structure in superconducting thin films of YBa2Cu3O6+x (YBCO) is optimized on a new type of IBAD-MgO based template by doping YBCO with non-superconducting BaCeO3 (BCO) and BaZrO3 (BZO). In these films, the YBCO is well ordered, no large angle grain boundaries are seen and the isotropic BCO particles are randomly distributed while the BZO grows as unidirectionally splayed and shortened nanorods. Additionally, the low-angle grain boundaries formed during the growth process have an impact on the flux pinning. The flux pinning behaviour can be explained by the vortex path model, where the pinning paths are shorter in BZO doped than in BCO doped films. In BZO doped films, the vortices are pinned with greater pinning force and thus the critical current density Jc is higher than in BCO doped films, especially in high magnetic fields, where the wide peaks in Jc(θ) were seen along the YBCO c-direction. This direction dependent pinning can be explained by the nearly similar diameters of BZO nanorods with those of vortices, thus efficiently increasing the vortex pinning in the vicinity of YBCO c-axis.