ENHANCEMENT OF THE FISHTAIL EFFECT IN THE DYBA2CU3O7-DELTA SINGLE-CRYSTAL AT MAGNETIC-FIELD TILTED FROM THE C-AXIS

We studied angular and temperature dependences of the irreversible mag netisation on a twin-free DyBa2Cu3O7-delta single crystal both before and after irradiation with Pb-ions, The irradiation produced columnar tracks along the c-direction which increased significantly the induced current density j(s). The fishtail effect observed before irradiation was shifted to higher temperatures but survived. At high fields (abov e 2.4 T) the magnetic hysteresis loops became flat, their height being nearly field independent. In the high-field range a distinct differen ce in the angular dependences of the unirradiated and irradiated sampl e was observed whereas at low fields the angular behaviour was qualita tively the same for both samples. This fact points to the qualitative difference in the flux pinning processes governing the high-field and central peak regions. The differences imply that the central peak migh t be mainly due to the in-plane components of the internal field in co ntrast to the high-field range where the c-axis component of the inter nal field predominates. (C) 1997 Academic Press Limited.