Vortex creep and critical current densitiesJ_cin a 2μm thick SmBa₂Cu₃O_7−dcoated conductor with mixed pinning centers grown by co-evaporation

Abstract

We report the critical current densities Jc and flux creep rates in a 2 μm thick SmBa2Cu3O7–δ coated conductor produced by co-evaporation. The sample presents strong pinning produced by correlated disorder (CD) (boundaries between growth islands, dislocations and twin boundaries) as well as random nanoparticles. Correlated pinning along the c-axis was evidenced due to the appearance of a large peak in the angular critical current, centered at H║c. The analysis of the critical current density Jc (with the magnetic field applied parallel (H║c) and at 45° of the c-axis (H║45°)) indicates that CD assists pinning throughout the temperature range. For all temperatures and at both angles the in-field dependence of Jc exhibits a power-law behavior. The contribution of CD drops when the field is rotated to intermediate angles between the c axis and a–b axis (i. e. H║45°), which derives in a reduction of the absolute Jc value and poorer in-field dependences. The flux creep rate depends on the angle and its values remain approximately constant within the power-law regime. For H║c and H║45° and for magnetic fields lower than 20 kOe, the flux relaxation presents characterizing glassy exponents μ = 1.70 and μ = 1.32, respectively.

Effect of mixed pinning landscapes produced by 6 MeV oxygen irradiation on the resulting critical current densities Jc in 1.3 µm thick GdBa 2 Cu 3 O 7- d coated conductors grown by co-evaporation

“…At temperatures below 40 K with H║c and H║45°, the critical current density J c with high magnetic field can be significantly improved by irradiation. For doses of 1x10 14…”

“…The formation of the desired pinning centers depends sensitively on the film deposition technique and substrate architecture [1,12,13,14]. Despite the remarkable advance in the synthesis of desirable microstructures obtained at laboratory scale research, pinning landscapes including a high density of strong and weak pinning centers are usually difficult at industrial scale.…”

“…As mentioned above, at the plateau on the µ glassy exponent. The vortex dynamics for pristine CCs usually displays µ ≈ 3/2[14,15,34] which successively decreases with doses. No theoretical predictions have been developed for the glassy exponents in mixed pinning landscapes.…”

Competition between pinning produced by extrinsic random point disorder and superconducting thermal fluctuations in oxygen-deficient GdBa2Cu3O x coated conductors

“…The exponent α is usually related to the type of pinning centers being≈0.5-0.62 for pinning produced by random nanoparticles [24]. Moreover, tapes growth on IBAD-MgO templates usually display correlated pining due to island boundaries [18,25]. The results indicate that J c sf decreases with the changes in x [13] and with irradiation [8].…”

In-field dependences of the critical current density J in GdBa2Cu3O7-d coated conductors produced by Zr irradiation and post-annealing at low temperatures

“…The pristine films display a pinning landscape with sphere-like and irregular precipitates (Gd 2 O 3 ) embedded in the GBCO matrix with typical diameter of approximately 50 nm [7]. In addition, correlated pinning produced by twin boundaries and boundaries between islands usually assists the pinning produced by the nanoparticles [13]. For proton and oxygen irradiation, the optimal doses result from a balance between the enhancement of the critical current densities J c and the suppression of the superconducting properties produced by the damage (reduces selffield J c ).…”