Abstract
The transport critical current density of bulk sintered samples of RBa2Cu3O7-x with R=Y, Gd, Ho, and Er has been determined at 77 K from I-V curves at different applied DC-magnetic fields (0<or=H<or=20 Oe), also the AC-susceptibility as a function of AC-field amplitude has been measured with a superimposed DC-magnetic field (0<or=H<or=30 Oe) at 77 K. The transport and magnetic (inductive) critical current densities, are clearly larger in field cooled samples than in zero field cooled samples. Likewise, the degree of shielding as determined from the AC-susceptibility measurements is larger for field cooled samples than for zero field cooled. This anomalous behaviour can be explained in terms of the magnetic flux trapped in the grains when the sample is field cooled, which leads to a decrease in the magnetic induction at the intergrain region and therefore to a higher intergranular critical current density compared to a zero field cooled sample.
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