A simplified approach to the temperature, frequency, and applied field variation in AC susceptibility measurements of bulk superconductors

Abstract

A qualitative model for the response of granular superconductors in AC magnetic fields is derived from first principles. By taking into account Faraday induced currents andfields due to time varying flux within the penetration depth and in the grain boundaries, an out-of-phase component, χ", appears in the AC magnetization. λ(T) and R(T) give rise to the χ" peak near T_c. The dependence of the shielding of the Josephson weak links on intergranular phase coherence gives rise to the χ" peak below T_c and the corresponding hump below T_c in χ'. Frequency and applied field dependence of the AC magnetization is discussed using this model.