Magnetic flux diffusion in high-Tc superconductors: step-response and AC-susceptibility

Theoretical calculations for the response of high-Tc ceramic superconductors to external magnetic field-step and ac excitations were performed. Despite our simplifying assumptions, the analytical solutions we obtain provide a clear insight into the flux penetration phenomenon in these materials. We discuss the characteristic time of flux penetration, the ac-susceptibility, and their dependence on field amplitude and frequency, Our results are in good agreement with experiments.