Pinning analyses on epitaxial YBa2Cu3O7−δ films with BaZrO3 inclusions

Abstract

The introduction of artificial pinning sites in YBa2 Cu3O7−d (YBCO) epitaxial thin films has been\ud obtained by pulsed laser deposition ͑PLD͒ technique from YBCO-BaZrO3 ͑BZO͒ composite targets\ud with BZO concentration ranging from 2.5 to 7 mol %. The typical critical temperature, Tc , drop\ud observed in YBCO-secondary phase films grown by PLD has been successfully recovered by\ud increasing the deposition temperature. Transport properties analyses revealed improved pinning\ud force values for YBCO-BZO films for BZO concentration above 5 mol %. These films exhibited an\ud anomalous dual peak structure which has been ascribed to the presence of two pinning\ud contributions. The crossover field, Bm , separating these two pinning regimes has been observed to\ud be temperature independent suggesting the occurrence of the matching field effect. The measured\ud value of Bm agreed with the matching field value, B⌽ = Knd⌽0 , as evaluated from transmission\ud electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making\ud YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below Bm in all\ud the temperature range inspected. On the contrary, in the high magnetic field range ͑above Bm͒, the\ud effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting\ud that at low temperatures the dominant pinning contribution arises from isotropic pinning centers

Effects of surface finish and mechanical training on Ni-Ti sheets for elastocaloric cooling

“…On the other hand, the YBCO-BYNTO film shows a more gradual drop, at a higher field value of around 5 T. From the evaluated column density n, an equivalent or matching field (magnetic field value as vortex density matches the defects density) can be evaluated by using B φ = nφ 0 , where φ 0 is the magnetic flux quantum and thus both YBCO films have a similar value B φ ∼ 5.2 T. Accordingly, in the YBCO-BYNTO film, the drop-off from the plateau-like behaviour at 5 T can be explained in terms of a matching field effect. 26 A similar J c behaviour was also observed for linear segmented nanorods formed by Ba 2 (Y/Gd)(Ta/Nb)O 6 20,22 even though in a narrower B range with the lower matching field B φ = 2.6 T evaluated. The lower-field drop (3.5 T) for the YBCO-BYTO film can be explained by the partial truncation of the BYTO nanocolumns, bringing less effective pinning of the vortices with respect to the continuous linear defects found in YBCO-BYNTO.…”

Directional Vortex Pinning at Microwave Frequency in YBa2Cu3O7−x Thin Films with BaZrO3 Nanorods

“…The results here presented can be well understood when the morphology of our YBCO/BZO sample is taken into account: in fact, TEM images clearly show the existence of correlated defects approximately parallel to the c-axis [14]. Thus, the behavior of vortex pinning as measured by r is fully consistent with very large correlated pinning along the c axis.…”

“…All the measurements were performed at selected temperatures, carefully chosen in order to avoid the substrate resonances caused by SrTiO 3 [11] . The BZO inclusions generated columnar-like defects, approximately perpendicular to the film plane, as observed with transverse TEM images [14], while such defects were not detected in pure YBCO samples. The measured T c (zero dc resistance criterion) was consistently ∼90 K in all samples.…”

Anisotropy and directional pinning in YBa2Cu3O7−x with BaZrO3 nanorods

“…With respect to dc studies, 1, [9][10][11] here, we exploit the dynamics at different time scales and we show that the anisotropic-mass angular scaling exists and is limited to intrinsic properties, such as the flux-flow resistivity q ff . By contrast, directional pinning arising from the nanorods and the layered structure dominates and completely destroys the angular scaling in pinning-related quantities.…”