COMPETING PINNING MECHANISMS IN BI2SR2CACU2OY SINGLE-CRYSTALS BY MAGNETIC AND DEFECT STRUCTURAL STUDIES

A correlation between magnetic hysteresis [measured with a vibrating-s ample magnetometer (VSM)] and defect structures (studied by transmissi on-electron microscopy) is reported for a number of Bi2Sr2CaCu2Oy sing le crystals in the as-grown state and after annealing in oxygen or vac uum above 400-degrees-C. Different regimes of flux pinning can be dist inguished from VSM measurements, which we associated with point defect s (oxygen vacancies) and planar dislocation networks. Dislocation netw orks observed in Bi2Sr2CaCu2Oy Single crystals provide effective pinni ng centers for decoupled two-dimensional (2D) pancake vortices, especi ally when the characteristic length scale of the network matches that of the 2D pancake vortex spacing. Anomalies in the magnetic properties are discussed in terms of the competition between pinning from point defects and dislocation networks, together with a transition from a 3D flux lattice to a 2D pancake vortex regime.