Orientation induced crossover in pinning force density and peak effect in Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8+x</SUB> single crystals

Magnetization-hysteresis measurements on single crystal of Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8+x</SUB> (Bi-2212) at various temperatures (20-40 K) are reported for different applied field orientations (θ) relative to the unit cell's c-axes. An orientation-induced crossover in the magnitude of the volume pinning force density F<SUB>p</SUB> around θ≥20° is observed which does not conform with predictions of the existing 2D-pancake model. The results further indicate that the 'peak-effect' in Bi-2212 is associated with the crossover in the vortex matter from a quasi-lattice to a disordered vortex solid