Flux Dynamics and Time Effects in a Carved out Superconducting Polycrystalline Bi-Sr-Ca-Cu-O Sample

Systematic slow transport relaxation (V-t curves) and magnetovoltage measurements (V-H curves) have been carried out in a carved out superconducting polycrystalline Bi-Sr-Ca-Cu-O sample as a function of current (I), temperature (T), and external field (H). The V-t curves reveal the details of the time evolution of the penetrated state within the granular structure of the sample and also give a direct evidence of the relaxation of the flux trapped inside the drilled hole on the time scale of the experiment. On the other hand, V-H curves exhibit several unusual interesting properties upon cycling of the external magnetic field in forward and reverse directions, and, in addition to irreversibilities, strong reversible effects are observed, which is associated with the trapping of the macroscopic flux bundles in the drilled hole. It is also observed that the field sweep rate influences dramatically the reversible and irreversible behavior of V-H curves. The experimental results were mainly interpreted in terms of current and field induced organization of the vortices.