Frequency dependence of the intergranular AC loss peak in a high-Tc Bi-(Pb)-Sr-Ca-Cu-O bulk superconductor

We have performed AC susceptibility measurements as a function of temperature; frequency and AC field amplitude on a rectangular bar shaped high-temperature superconductor with nominal composition of Bi1.8.4Pb0.34Sr1.91Ca2.03Cu3.06O10 prepared by the liquid ammonium nitrate method. We have observed that as the frequency (AC field amplitude) increases, the intra- and intergranular AC loss peaks move higher (lower) temperature, which indicates that AC losses are due to both hysteretic bulk pinning losses and viscous (flux flow) losses. M-H curves exhibit a hysteresis which is similar to that of hysteretic superconductors. Activation energy at the grain boundary is extracted from the loss peak at some selected AC fields. Experimental results are qualitatively discussed in the framework of the critical state model (CSM). (C) 1998 Elsevier Science B.V. All rights reserved.