Three-dimensional vortex pinning by nano-precipitates in a Sm-dopedYBa2Cu3O7−x coated conductor

Abstract

We report on the thickness and angular dependence of the critical current densityJc(H,θ), the irreversibilityfield Hirr, and thebulk pinning force Fp(H) of a metal-organic chemical vapour deposition (MOCVD) grownYBa2Cu3O7−x (YBCO) coatedconductor, which contains ∼17 vol% of ∼10 nm sized(Y,Sm)2O3 precipitates with anaverage spacing of ∼10–15 nm. Some surface porosity and amorphous second-phase particles on the scale of∼0.5–1 µm appear to reduce the current-carrying cross-section, which controls the magnitude ofJc but not the vortex pinning. We observed an enhancedHirr∼9 T at 77 K alongthe c-axis which,like the shape of Jc(H) and Fp(H), was independent of thickness as the sample was milled down to∼0.16 µm. Angular-dependentmeasurements of Jc showed the usual excess vortex pinning along thec-axis andalong the ab-plane, but with a background that could only be fitted with anunusually small anisotropy parameter of 3, which, like the highHirr and the thickness-independent shape ofFp(H), we ascribe to strong vortex pinning centre interactions. Together, these measurements showvery different behaviour from most pulsed-laser-deposited films, which exhibit strongthickness-dependent properties. We ascribe the present different results to the dense arrayof small, insulating precipitates, which act as strong pinning centres and produce strongthree-dimensional (3D) vortex pinning, because their separation of 10–15 nm is always muchsmaller than the film thickness.