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

In order to focus on the effectiveness of surface columnar defects (SCDs) i n bulk materials we have analysed the magnetic properties of melt-textured YBa2Cu3O7-delta samples, irradiated on opposite sides by means of 2 GeV gol d ions. The irradiation affects the 10% of the whole volume. The same ion d ose was implanted in two samples, the first one exhibiting a defect landsca pe 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 an d a significant damage in the sample exhibiting a fishtail effect. An analy sis of the volume pinning forces is performed, with the purpose of discrimi nating the effects of the different kinds of defects. We found that each ki nd of defect changes its role after irradiation, as well as across the phas e diagram. The changes are determined by mechanisms of either correlation o r competition between SCDs and other intrinsic defects. (C) 2001 Elsevier S cience B.V. All rights reserved.