Large fishtail effect in DyBa 2Cu 3O 7−δ single crystals containing columnar defects

Abstract

Using capacitance torque magnetometry, hysteresis loops were measured on a Pb-ion irradiated DyBa 2Cu 3O 7−δ single crystal as a function of magnetic field, temperature and angle Θ between the field direction and the c axis of the sample. The superconducting current densities, j c ( T, B, Θ), determined using the extended Bean model, show a clear fishtail effect at temperatures above 30 K despite the large enhancement of j c due to the columnar tracks. The enhancement of j c due to irradiation was magneto-optically determined to j c ( φt)/ j c (0) = 10 at T = 30 K. The pinning energy U 0 is, however, only slightly increased by the irradiation. Our measurements indicate clearly that the fishtail effect is a general feature of the high- T c superconductors and not related to a special arrangement of pinning centres.