Magnetization relaxation in the flux-creep annealing regime across the second magnetization peak of disordered YBa 2Cu 3O 7− x crystals

Abstract

The relaxation of the irreversible magnetization of disordered YBa 2Cu 3O 7− 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 crossover to a dissipation process involving the plastic deformation of the vortex system. In our experiments, the vortex creep process appears to be exclusively controlled by collective pinning barriers (diverging at low current densities) only below the onset of the SMP, where the vortex system is stable against dislocation formation. The (elastic) collective pinning barriers observed for magnetic field values close to the onset of the SMP (where the plastic barriers are high) could be related to the recently proposed collective 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.