Orientation-induced crossover in pinning force density and peak effect in Bi2Sr2CaCu2O8+x single crystal

Magnetization-hysteresis measurements on single crystal of Bi2Sr2CaCu2O8+x (Bi-2212) at various temperatures (20-40 K) an reported for different appli ed field orientations (theta) relative to the unit cell's c-axes. An orient ation-induced crossover in the magnitude of the volume pinning force densit y F-p around theta greater than or equal to 20 degrees is observed which do es not conform with predictions of the existing 2D-pancake model. The resul ts further indicate that the 'peak-effect' in Bi-2212 is associated with th e crossover in the vortex matter from a quasi-lattice to a disordered vorte x solid. (C) 1999 Elsevier Science B.V. All rights reserved.