Angle dependent magnetization measurements have been carried out to investigate the role of grain boundaries (GBs) on the flux-line lattice (FLL) of high quality Bi2Sr2CaCu2O8+y (BSCCO) single crystals. We find that the microscopic evidence of GBs are responsible for unidirectional pinning below 1 T in as-grown crystal at 20 K. However, the unidirectional pinning observed in BSCCO crystal irradiated with 200 MeV Ag-ions can exist beyond 5 T at 20 K due to columnar tracks which act as effective pinning centres. Copyright (C) 1996 published by Elsevier Science Ltd
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