Temperature dependence of the low-field magnetization of granular superconductors

Calculations of low-field magnetization curves of superconducting granular systems an carried out by means of a critical-state model that follows from the Josephson-junction network description of this class of superconductors. An approximate analytical expression of the temperature-dependent effective critical current density J(c) is derived. General critical-state calculations which explicitly take account of temperature effects are thus specified to the case of a cylindrically symmetric polycrystalline superconducting sample. The calculated low-field magnetic properties are seen to be in good agreement with experimental results.