Flux Creep of Melt Processed YBCO

Abstract

Flux creep measurements are very informative in understanding the pinning characteristics of type II superconductors. In many creep experiments of high temperature superconductors, logarithmic time decay of critical current or magnetization is observed. This seems to fit a very simple flux creep model based on thermally assisted flux motion. However, the pinning energies obtained from simple Arrhenius plots do not fit the theoretical model that the pinning energy increases with decreasing temperature. This mismatch is ascribed to the fact that the effective pinning barrier is not linear to the current. In this paper, we measured flux creep of three melt processed YBCO with different Jc values under various conditions and found that the effective pinning barrier (Ueff) is not proportional to 1-(J/Jc). It has also been found that if we draw entire Ueff-J curves, the results of flux creep measurements could clearly be explained in terms of flux pinning and were consistent with the idea that the pinning energy is larger in the samples with larger Jc values.