AC SUSCEPTIBILITY HYSTERESIS IN GRANULAR SUPERCONDUCTORS

We have investigated the hysteresis in the AC susceptibility of granul ar YBCO superconductors when the DC field is cycled. A crossover point is observed where the susceptibility chi' in decreasing fields become s more diamagnetic than for increasing fields, and this is investigate d as a function of temperature, AC field amplitude and frequency. The behavior is consistent with the variation of the AC penetration depth with these variables and with a reduced flux density of the intergrain regions on field reversal. The zero field cooled behavior of the seco nd harmonic chi(2) as well as the behavior of chi' in field cooled con ditions, are also reported. The DC field dependence of chi' is analyze d using the low amplitude, linear response region approximations.