On the sensitivity of the Maley technique for the analysis of vortex-creep activation energy in disordered superconductors

Abstract

We performed magnetization relaxation experiments for optimally doped YBa2Cu3O7−δ (YBCO) films with the external magnetic field H = 20–30 kOe oriented along the c axis and at relatively low temperatures T = 10–32 K, where a crossover elastic (collective) vortex creep–plastic creep is expected. The creep crossover is generated in this case by the T dependent macroscopic currents induced in the specimen, and manifests itself through the occurrence of a maximum in the current density J (or T) variation of the normalized vortex-creep activation energy U*, at which the creep exponent changes sign. With the same magnetization relaxation data the widely used Maley technique to construct the J dependence of the vortex-creep activation energy U supplies an U(J) variation close to the logarithmic one. It appears that the Maley technique may lead to unreliable results, due to the creep crossover characteristic to standard zero-field-cooling magnetization measurements and the reduced overall relaxation (in a convenient relaxation time window) for highly disordered specimens. It is suggested that the results obtained with this scheme should be checked by determining the U*(T,J) variation.