Crystal Growth Direction Dependence of Microstructure and Superconducting Properties of Cylindrical RE123 Melt-Solidified Bulks

In our previous study, the c-growth region of the RE123 melt-solidified bulks was found to exhibit huge second peak effect in their magnetization hysteresis loops, reflecting the improved J_c properties under high fields compared with their a-growth region. The cylindrical Ho123 bulks containing Pt (0.5 wt.%) and CeO₂ (1 wt.%) were synthesized by the melt-solidification method using cold-seeding technique in the present study. These bulks are composed of c-growth regions as major parts. Dispersion of Ho211 particles, crystallinity of the Ho123 matrix and J_c characteristics were systematically studied for the a- and c-growth regions of the bulks. In the c-growth region just below the seed crystal, the volume fraction of Ho211 particles was lower than in the a-growth region, while this part showed huge second peak effect. However, the c-growth region maintained higher J_c than that of the a-axis region even at the positions far from the seed crystal, where the mean particle size and volume fraction of Ho211 were almost identical to those in the a-growth region. These preferable J_c properties observed in the c-growth region can be explained by excellent crystallinity of the Ho123 matrix with few low-angle subgrain boundaries