MAGNETIC FIELD AND HISTORY DEPENDENCE OF THE HARMONIC SUSCEPTIBILITY IN A GRANULAR SUPERCONDUCTOR

We report on the generation of harmonics of the ac susceptibility in a typical Y(123) granular superconductor. The intergrain harmonic response has been studied at T=77 K as a function of the ac field, both with and without superposed dc fields. We find that our results can be adequately described by the Anderson-Kim model. The effect of superposed dc fields on the ac field dependence of the even and odd harmonics has been qualitatively explained. Magnetic history dependence has ben studied in the field cooled and remnant states. Effects of field cooling indicate that the intergrain fields in this case are slightly smaller than for the corresponding zero field cooled condition. Remnant field studies clearly show the role of trapped flux in generating even harmonics.