NUMERICAL CALCULATIONS OF IMAGINARY SUSCEPTIBILITY IN THE INTERGRAIN REGION OF GRANULAR SUPERCONDUCTORS

Abstract

Using a critical state model for the intergrain critical current density (J _c ) of a granular superconductor in which the grains are separated by Josephson junction type weak links, numerical calculations of the imaginary part of the complex susceptibility (χ″) and the ac losses (W) are performed. The dependences of the imaginary susceptibility on the amplitude of the external magnetic field (H_ac), grain size (R _g ), barrier width (d), lower critical field (H _cl ), normal resistivity of the junction (ρ_j) and temperature (T) are discussed. We also comment on a minimum in the hysteretic ac losses when a constant magnetic field (H_dc) is superimposed on the alternating field. Some comparison with experimental data is made.