Large fishtail effect in DyBa2Cu3O7-delta single crystals containing columnar defects

Using capacitance torque magnetometry, hysteresis loops were measured on a Pb-ion irradiated DyBa2Cu3O7-delta single crystal as a function of magnetic field, temperature and angle circle minus between the field direction and the c axis of the sample. The superconducting current densities, j(c)( T, B, circle minus), 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)(phi t)/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.