Pinning properties of quenched and melt growth method-YBCO bulk samples

A comparison between two different irradiation effects was accomplished on bulk YBCO samples synthesized with the quenched and melt growth method (QMG -YBCO) to investigate strong pinning properties. High-energy proton-irradia tion introduces small defects comparable to unit cell size into the sample, and they act as effective pinning centers for all temperature range in low field around I T. No enhancement, however, can be seen in higher field ran ge. The defects introduced with the irradiation reinforce the pinning prope rties of preexisting pinning centers randomly distributing in the sample. C olumn-like defects with 3.5 GeV Xe-irradiation were introduced but the pinn ing properties show no significant enhancement except higher temperature re gion. This indicates that pre-existing pinning centers are strong enough th an the columnar defects. In higher field region, the contribution of column ar defects for pinning becomes relatively large. For both irradiation cases , almost pinning properties are determined by the pre-existing pinning cent ers. (C) 2001 Elsevier Science B.V. All rights reserved.