The effects of artificial holes with different diameters on the surface magnetic properties in YBCO superconductor

Bulk YBCO superconductor was manufactured with the top-seeded melt grown method. In order to elucidate the effects of defects in YBCO, the melt-textured superconductor was arbitrary drilled by mechanical tool on the surface along c-axis. Typical artificial hole diameters were 0.5, 0.7 and 1.0 mm, respectively. Based on the measurements of magnetic flux mapping and levitation force, we conclude that the magnetic field trapping capacity decreased systematically with increasing the diameters of hole. The maximum magnetic flux density of the sample without any holes was 0.05 T, while the maximum magnetic flux density of sample with 1.0 mm hole in diameter was very low as around 0.023 T.