Collective Creep Model Research Articles

Flux motion in Bi and Tl — based superconductors

Abstract The time decay of the magnetization was studied on Tl — Ba -Ca — Cu -O and Bi ( Pb ) — Sr — Ca — Cu — O superconductors. In the Tl — based compound, the results provide evidence for a non thermally activated flux motion at low temperature suggesting quantum tunneling of vortices. In the Bi- based compound a crossover, with increasing temperature, from logarithmic to non logarithmic decay regime, is found according to the collective creep model.

Time dependence of the magnetization in Bi 2Sr 2CaCu 2O 8+z

The Maley procedure has been applied to obtain U eff(j) of a Bi-n = 2 single crystal for B < 4 T//c-axis and T < 20 K from the time dependence of the non-equilibrium magnetization. Analyzing the resulting U eff (j) within the collective creep model it is found that for large current densities, flux creep of elastic small (< λ) flux bundles consisting of quasi 2-dimensional pancake vortices occurs. However, at large j better agreement is found with the logarithmic potential model. From the logarithmic U eff(j) dependence j c in the absence of thermal activation has been derived. It has been found that j > 10 10 Am −2 for all fields investigated. These high values of j c indicate that the pancake vortices are pinned independently and that oxygen vacancies in the CuO 2 planes are not the only pinning centers.