Flux pinning by columnar defects in Bi₂Sr₂CaCu₂O_8+y single crystals

Abstract

We report the magnetization studies of as-grown and 200 MeV Ag-ion irradiated BSCCO single crystals. The maximum shift of the irreversibility line was observed for fluence level of 2.5 × 10¹¹ ions/cm² with a corresponding B_Φ = 5 T. Ag irradiation induces damage in the form of amorphous columnar tracks which penetrate throughout the thickness of the crystal. These defects are not only responsible to shift the irreversibility line but also make the dislocation networks present in the CuO₂ plane ineffective and hence the disappearance of the double-peak anomaly generally observed in the as-grown crystal. The angle dependence of the irradiated BSCCO crystal predicts the presence of unidirectional pinning and interlayer Josephson coupling. The 2D pancake vortices are not completely decoupled even up to T = 50 K. The magnetic relaxation in BSCCO crystals predicts the enhanced pinning upon irradiation and the line behaviour of flux-lattice which can exist up to high temperature. The pinning energies calculated using predicted Anderson-Kim model shows enhanced pinning energy upon irradiation. The columnar defects by heavy-ion irradiation have been proved to be an effective tool for enhancement of flux-pinning. Even after heavy-ion irradiation 2D nature of BSCCO crystal is preserved.