Abstract
The relaxation of the irreversible magnetization of optimally doped YBa2Cu3O7−δ (YBCO) films and YBa2Cu3O7−δ/PrBa2Cu3O7−δ (YBCO/PrBCO) superlattices in a magnetic field H oriented along the c axis was investigated over a large temperature T interval. The observed behavior is dominated by the presence of a crossover elastic vortex creep at low T–plastic creep at high T generated by the T-dependent current density J of the macroscopic currents induced in the specimen during experiments. Magnetization relaxation in the flux-creep annealing regime indicates the reduction of the creep crossover temperature with decreasing J, which suggests that in static conditions the disordered vortex phase at high H behaves like a plastically pinned vortex assembly, rather than an elastic vortex glass. The often reported scaling of the electric field E–transport current density J characteristics in agreement with an elastic vortex glass–vortex fluid transition seems to originate from the creep crossover generated by an increasing J.
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