Three-dimensional vortex pinning by nano-precipitates in a Sm-doped YBa₂Cu₃O7−xcoated conductor

We report on the thickness and angular dependence of the critical current density J c ( H ,θ), the irreversibility field H irr , and the bulk pinning force F p ( H ) of a metal-organic chemical vapour deposition (MOCVD) grown YBa 2 Cu 3 O 7− x (YBCO) coated conductor, which contains ∼17 vol% of ∼10 nm sized (Y,Sm) 2 O 3 precipitates with an average 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 of J c but not the vortex pinning. We observed an enhanced H irr ∼9 T at 77 K along the c -axis which, like the shape of J c ( H ) and F p ( H ), was independent of thickness as the sample was milled down to ∼0.16 µm. Angular-dependent measurements of J c showed the usual excess vortex pinning along the c -axis and along the ab -plane, but with a background that could only be fitted with an unusually small anisotropy parameter of 3, which, like the high H irr and the thickness-independent shape of F p ( H ), we ascribe to strong vortex pinning centre interactions. Together, these measurements show very different behaviour from most pulsed-laser-deposited films, which exhibit strong thickness-dependent properties. We ascribe the present different results to the dense array of small, insulating precipitates, which act as strong pinning centres and produce strong three-dimensional (3D) vortex pinning, because their separation of 10–15 nm is always much smaller than the film thickness.