Transport critical current density of polycrystalline YBCO in zero field cooled and field cooled states: a comparison

Magnetic field dependence of transport critical current density (J<SUB>c</SUB>) of a polycrystalline YBCO superconductor in field cooled and zero field cooled cases have been studied experimentally. The measured J<SUB>c</SUB> value when the sample was cooled in a field (FC) was always larger than that measured for a zero field cooled (ZFC) case in the same magnetic field. We also observe (i) a peak in the field dependence of the ratio of J<SUB>c</SUB> in FC case to that of ZFC case and (ii) an anomalous rise in J<SUB>c</SUB> in ZFC case with increasing field. These observations are explained as a signature of two types of regions (intergrain and intragrain) in sintered specimens