Effect of the configuration of the trapped flux on the decay rate of remanent magnetic moments in type II superconductors

Several workers have measured the rates of decay of remanent magnetic moments in granular high-T-c superconductors where the temperature-field histories generated trapped flux profiles comprising two concentric regions of countercirculating persistent currents. Exploiting a simple model based on the critical state for bulk specimens and the conservation of flux for the redistribution of vortices, and neglecting H-c1, we account for the major features of these observations although in some cases the number of trapped vortices is small. The model makes readily testable predictions of the relative magnitudes of the initial rates of magnetic relaxation for various configurations of flux density profiles.