Influence of surface barriers on vortex dynamics in Bi2Sr2CaCu2O8+δ whiskers

Bi2Sr2CaCu2O8+δ whiskers are single crystals with highly regular surfaces and few extended defects, making them excellent model systems for studying the role of surfaces in magnetization. Furthermore, they can be elastically bent without losing their superconducting properties, making them potentially important technological materials. We have made a detailed investigation of their magnetic properties using micron-sized Hall probe arrays and show that surface effects play a dominant role in controlling the vortex dynamics, particularly in the moderate to high temperature regime. Local magnetic induction cycles exhibit the asymmetric behaviour characteristic of surface barriers and when the whiskers are slowly field cooled, sharp jumps are observed. The systematic behaviour of these jumps leads us to speculate that they represent sudden configurational rearrangements as a result of the interplay between vortex-surface barrier and vortex-vortex interactions.