Vortex creep in TFA–YBCO nanocomposite films

Abstract

Vortex creep in YBa 2 Cu 3 O 7 − x (YBCO) films grown from the trifluoracetate (TFA) chemical route with BaZrO 3 and Ba 2 YTaO 6 second-phase nanoparticles (NPs) has been investigated by magnetic relaxation measurements. We observe that in YBCO nanocomposites the phenomenological crossover line from the elastic to the plastic creep regime is shifted to higher magnetic fields and temperatures. The origin of this shift lies on the new isotropic-strong vortex pinning contribution appearing in these nanocomposites, induced by local lattice distortions. As a consequence, we demonstrate that the addition of non-coherent NPs produces a decrease in the creep rate S in most of the phase diagram, particularly, in the range of fields and temperatures ( > T 60 K, μ > H 0.5 T 0 ) relevant for large scale applications.

Large pinning forces and matching effects in YBa2Cu3O7-δ thin films with Ba2Y(Nb/Ta)O6 nano-precipitates

“…Larger splay values lead to lower creep rates and therefore higher J c values but no observable matching effects. Similar reductions in creep rate due to additional defects in YBCO films have been reported recently for increased film thickness and substrate decoration53, and nanoparticle addition (Y211, BZO, BYTO) in films grown by metall-organic deposition (MOD)5455. In our samples, we observe high J c values and matching effects.…”

Angular flux creep contributions in YBa2Cu3O7−δ nanocomposites from electrical transport measurements

“…As regards the temperature dependence, besides the monotonic increase of S with increasing temperature, we observe an S(T) peak appearing in the region that comprises 50 K to 80 K, especially notable for the pristine sample and nanocomposite C. For nanocomposite B, the one with more SFs, the peak reduces or even vanishes at low magnetic field, confirming that the presence of artificially induced SFs modifies the structure of the CuO 2 planes and its effect on thermal activation, obtaining lower creep rates for a large range of temperatures. Similar S(T)-peaks (also called S(T)-dips in other works, since both shapes occur concurrently with each other) have been observed in YBCO single crystals and thin films, attained by inductive measurements for H||c, where the peak has been attributed to the generation and expansion at no energy cost of vortices, mediated by double-kink (DK) thermal excitations in correlated pinning sites as columnar defects 6,17 , twin boundaries 8,18 , or by a similar effect described in nanoparticles, where the vortex line slides along the surface of the nanoparticle 9 . We propose by the following explanation, that DKs also account for the S(T)-peak arising for H||ab, aided by the periodical and regular IP originated between the superconducting CuO 2 planes (depicted in Fig.…”

Optimal Vortex Pinning in YBa2Cu3O7-x Superconducting Films Up to Very High Magnetic Fields

“…At intermediate T and high H: a high density of anisotropic strong defects with a very long vertical coherence (like long twin boundaries in thick nanocomposites or elongated nanorods), if possible combined with other auxiliary strong or weak isotropic defects in order to sum pinning gains and avoid vortex creep excitations in parallel correlated defects 36,45,74 .…”