Mechanisms of weak thickness dependence of the critical current density in strong pinning ex situ metal-organic-deposition route YBa2Cu3O7-x coated conductors

TL;DR

This study investigates the weak thickness dependence of critical current density in high-quality YBa2Cu3O7-x coated conductors made by an ex situ metal-organic deposition process, revealing strong 3D vortex pinning as a key factor.

Contribution

It demonstrates that in ex situ metal-organic deposited films, Jc shows only weak dependence on thickness due to effective 3D vortex pinning, contrasting with in situ PLD films.

Findings

Jc weakly depends on film thickness despite porosity.

Local vortex-pinning Jc exceeds 5 MA/cm2.

Strong 3D vortex pinning causes vortex segmentation.

Abstract

We report on the thickness dependence of the superconducting characteristics including critical current Ic, critical current density Jc, transition temperature Tc, irreversibility field Hirr, bulk pinning force plot Fp(H), and the normal state resistivity curve measured after successive ion milling of ~ 1 um thick high Ic YBa2Cu3O7-x films made by an ex situ metal-organic deposition process on Ni-W rolling-assisted biaxially textured substrates (RABiTS). Contrary to many recent data, mostly on in situ pulsed laser deposition (PLD) films, which show strong depression of Jc with increasing film thickness t, our films exhibit only a weak dependence of Jc on t. The two better textured samples had full cross-section average Jc,avg(77K,0T) ~ 4 MA/cm2 near the buffer layer interface and ~3 MA/cm2 at full thickness, despite significant current blocking due to ~30% porosity in the film. Taking account of the thickness dependence of the porosity, we estimate that the local, vortex-pinning current density is essentially independent of thickness, while accounting for the additional current-blocking effects of grain boundaries leads to local, vortex-pinning Jc values well above 5 MA/cm2. Such high local Jc values are produced by strong three-dimensional vortex pinning which subdivides vortex lines into weakly coupled segments much shorter than the film thickness.