Depth-dependent critical-current density of melt-processed Y-Ba-Cu-O discs determined by the third-harmonic technique: Surface barrier and intrinsic pinning

• Third harmonic technique is modified for measuring depth dependent Jc of bulk superconductor.
• Surface damage and reduced effect of surface barrier and intrinsic pinning are found in melt-processed YBCO discs.
• Experimental findings are explained by existing models.

The critical-current density Jc of three Y-Ba-Cu-O (YBCO) discs, each cut from the upper section of a melt-processed single grain, has been determined as a function of the depth from the top (seeded) and bottom surfaces of the sample by a modified version of the inductive third-harmonic technique proposed originally by Mawatari et al. It is shown that local Jc in the vicinity of the bottom surface of the sample is lower than that in the vicinity of the top surface for thicker discs and there are reduced effect of surface barrier and intrinsic pinning and important surface damage. The technique employed is recommended as a tool for detecting the imperfection within superconducting structure in bulk YBCO.