Separation of enhanced and residual pinning mechanisms in single-crystal Bi2Sr2CaCu2O8+δ irradiated with heavy ions

Magnetization measurements have been performed on both pristine, as-produced single crystals of Bi2Sr2CaCu2O8+delta and on crystals irradiated with energetic heavy ions. A scaling analysis applied to the hysteresis curves measured for both crystals enables the enhanced contribution to the critical current, due to the columnar defects, to be separated from that due to the residual pinning. Magnetic hysteresis, due to pinning almost entirely by the columnar defects, can be scaled between 4 K and 40 K, suggesting that the irradiation damage results in a single pinning mechanism over this temperature range. A temperature-dependent crossover held B-cr is determined, above which pinning due to the columnar defects is dramatically reduced. B-cr rises to several times the matching held B-phi at low temperatures. These results indicate that pinning due to both types of defects appears as a linear summation in the overall pinning force and emphasizes the importance of both residual pinning and vortex-vortex interactions for fields close to B-phi where a crossover from correlated to point disorder determined behavior is usually assumed.