Low field flux dynamics of Pr-doped Bi-2212 single crystals

Abstract Magnetic hysteresis M(H,T) and magnetic relaxation M(t) results on various Pr-doped single crystals Bi 2 Sr 2 Ca 1−x Pr x Cu 2 O 8+δ are reported. Superconducting H-T phase diagram with applied field parallel to single crystal c-axis indicates that with progressive Pr doping from optimum composition (x = 0.11, T c = 88 K) to underdoped single crystal (x > 0.11), all characteristic field lines in H-T diagram shift to lower reduced temperature T/T c and lower field region with narrower second peak (H 2p ) window. Low field magnetic relaxation data near H 2p indicates a distinct change of flux creep behavior from collective creep model for field smaller than second peak onset field (H on ) to vortex glass model for H > H on . Such a crossover behavior implies a change in vortex coupling mechanism from vortex quasi-lattice to entangled vortex glass.