Jc–B characteristics for bulk single domain YBCO superconductors

We have studied the dependence of the magnetic critical current densities (Jc) on the applied field for the samples taken from various positions of a single domain YBCO disk. For most of the measured samples the Jc–B curves exhibited the peak effect at field of around 0.8 T, and the highest Jc value at 1 T and 77 K was found in the position of about 4.5 mm depth away from the surface of the disk. For various positions the features of Jc(B) curves were different. It is suggested that the peak effect is attributed to the field induced pinning of weak superconducting regions due to very wide superconducting transition as well as the distributions of the second phase particles. For the bulk sample the Jc(B) performance is inhomogeneous in the entire body.