Trapped field of YBa₂Cu₃O₇ QMG bulk magnets

Trapped field distributions of quench melt grown (QMG) bulk magnets were measured in several external fields and temperatures. QMG bulk superconducting material was made by a modified QMG process. The size of the QMG magnets was 46 mm in diameter and 15 mm in thickness. The QMG bulk magnets were magnitized by application and reduction of an external magnetic field from 3.5 T after cooling at several temperatures. The field distributions were measured by scanning a Hall probe or aligned Hall probes over the magnet surface. Maximum trapped fields at 77, 63, 50, 20 and 10 K were 1.08, 2.72, 3.07, 3.27 and 3.26 T, respectively. From these distribution shapes, it appears that maximum fields at temperatures lower than 50 K were limited by the applied external field of 3.5 T. At 77 K and high external field, 4-fold symmetry was observed in the field distribution. Flux jumps were observed at 10 K, although mechanical damage was not observed during these experiments. From these results it was found that the QMG bulk magnets can trap at least 3 T steadily at a temperature higher than 20 K and lower than 50 K.