Correlation and competition between surface columnar defects and intrinsic defects in melt-textured YBCO

In order to focus on the effectiveness of surface columnar defects (SCDs) in bulk materials we have analysed the magnetic properties of melt-textured YBa(2)Cu(3)O(7-delta) samples, irradiated on opposite sides by means of 2 GeV gold ions. The irradiation affects the 10% of the whole volume. The same ion dose was implanted in two samples, the first one exhibiting a defect landscape without intrinsic correlated disorder, the second one exhibiting slight fishtail patterns, interpreted as a signature of some intrinsic correlated disorder. The effect of the irradiation is a significant enhancement of the critical current in the sample not exhibiting intrinsic defect ordering and a significant damage in the sample exhibiting a fishtail effect. An analysis of the volume pinning forces is performed, with the purpose of discriminating the effects of the different kinds of defects. We found that each kind of defect changes its role after irradiation, as well as across the phase diagram. The changes are determined by mechanisms of either correlation or competition between SCDs and other intrinsic defects. (C) 2001 Elsevier Science B.V. All rights reserved.