Spatial inhomogeneities of Gd-Ba-Cu-O bulk superconductors evaluated by different Hall probe scanning methods

We studied spatial inhomogeneities of Gd-Ba-Cu-O bulk superconductors by using two different types of Hall probe scanning methods. One is a conventional scanning Hall probe (SHP) method, which can measure the trapped flux density distribution of superconductors after magnetized by external fields. The other is a recently developed magneto-scan method, which scans a Hall probe together with a permanent magnet and can detect shielding behavior of the sample surface without applying an external field. In the SHP method, the flux density distributions obtained by the field cooling (FC) scan were compared with those in the zero field cooling (ZFC) scan. It was found that the ZFC scan can acquire much more information on the sample inhomogeneity than the FC scan. The magneto-scan method was also adopted to the characterization of the same sample. It was found that this method was more sensitive than the SHP method, and allowed us to clearly detect some degradations in the vicinity of the seed crystal in the sample surface.