TEMPERATURE, FIELD AND FREQUENCY-DEPENDENCE OF INTERGRANULAR AC LOSS IN HIGH-TEMPERATURE SUPERCONDUCTORS

AC susceptibility studies have been performed to determine the dependence on temperature (4.2-120 K), AC magnetic field amplitude (0.01-10 G), and frequency (0.02-10 kHz) of the intergranular component, chi"(J), of the imaginary part of the susceptibility of polycrystalline YBa2Cu3O7 and Bi1.6Pb0.4Sr2Ca2Cu3O10 specimens. The intergranular loss peak temperature, T(p), shifts significantly to low temperatures with increasing field, and marginally to higher temperatures with increasing frequency. From the field and frequency dependence of T(p) we determine the intergranular critical current density, J(CJ), and the intergranular pinning potential U0(T = 0, H(ac) = 0). From the onset of the hysteresis loss we determine the irreversibility line.