ENERGY-DISSIPATION AND FLUX TRAPPING IN A HIGH-TC SUPERCONDUCTOR IN LOW AC AND DC MAGNETIC-FIELDS

The results of measurements of low frequency AC losses in a cylindrica l YBa2Cu3O7-x sample subjected to a sinusoidally varying magnetic fiel d, with a coaxially superimposed DC-bias field, are presented. It is f ound that magnetic history effects are not observed if only the AC fie ld is applied. A quite different behavior is observed if a DC magnetic field is trapped in the sample. In such a case, a significant increas e, above one order of magnitude, of the intergranular loss is observed , whereas the dissipation inside the granules is practically unchanged . Moreover, there exists a threshold value of the applied DC magnetizi ng field, below which changes of the AC losses are not observed. Its v alue is approximately equal to the first penetration field for the gra ins.