The dependence of pinning properties on superconducting layer thickness in IBAD/PLD YBCO-coated conductors

The thickness dependence of pinning properties is investigated in detail under various conditions of temperature, magnetic field and electric field for IBAD/PLD YBCO-coated conductors. The thickness-dependent critical current density in the three-dimensional pinning regime at low magnetic fields is attributed to the change in the morphology of the superconducting layer. It is found that while the irreversibility field increases with the thickness at low electric fields according to DC magnetization measurements, it decreases at usual electric fields corresponding to resistive measurements. This can be explained by the theoretical model of flux creep and flow with the irreversible thermodynamic principle that the transverse flux bundle size is determined so that the critical current density under the flux creep is maximized. The former model assumes the limitation of the longitudinal flux bundle size by the superconducting layer thickness, while the latter principle assumes a change in the transverse one from the value expected from the elasticity of flux lines. The observed n-value, the parameter describing the relationship between the electric field (E) and the current density (J) as , increases monotonically with the thickness in both electric field regions. This can be simply attributed to the increase in the pinning potential with the thickness.