MAGNETIC-FLUX DISTRIBUTION AND MAGNETIC-RELAXATION IN POLYCRYSTALLINE BI,PB-SR-CA-CU-O SUPERCONDUCTORS

We have studied magnetic flux distribution and magnetic relaxation in polycrystalline (Bi,Pb)2Sr2Ca2Cu3O10+x superconductors at 77 K using a movable miniature Hall sensor. Flux distribution was studied by measuring magnetic field profiles as a function of external field and time. The effects of inter- and intragrain shielding currents on magnetic flux distribution were distinguished using these measurements. The intergrain critical current density can be calculated from the field profile also in the case where intragrain currents are present. The relaxation of inter- and intragrain currents was distinguished and studied. The relaxation was logarithmic in both current systems. The relaxation rates of intergrain currents were remarkably higher than the rates of intragrain currents. When neither internor intragrain currents dominated, the total relaxation was non-logarithmic.