Magnetization relaxation in the flux-creep annealing regime across the second magnetization peak of disordered YBa2Cu3O7-x crystals

The relaxation of the irreversible magnetization of disordered YBa2Cu3O7-x crystals measured in the "flux-creep annealing" regime reveals that across the second magnetization peak (SMP) the barriers against flux motion remain finite at low current densities, which supports the existence of a crossov er to a dissipation process involving the plastic deformation of the vortex system, In our experiments, the vortex creep process appears to be exclusi vely controlled by collective pinning barriers (diverging at low current de nsities) only below the onset of the SMP, where the vortex system is stable against dislocation formation. The (elastic) collective pinning barriers o bserved for magnetic field values close to the onset of the SMP (where the plastic barriers are high) could be related to the recently proposed collec tive pinning of individual dislocations. The proliferation of dislocations across the SMP leads to liquid-like behavior of the disordered vortex phase in the vicinity and above the peak field. (C) 2001 Elsevier Science B.V. A ll rights reserved.