Abstract
Magnetic hysteresis M( H) and magnetic relaxation M( t) results on Pr-doped single-crystal Bi 2Sr 2Ca 0.89-Pr 0.11Cu 2O 8+ δ with optimum T c=88 K are reported. Superconducting H– T phase diagram with applied field parallel to single-crystal c-axis indicates that in the mixed state the anomalous second peak field and its onset field H 2p/ H on varies from 900/800 G at 15 K to 210/85 G at 40 K with a plateau around 20–30 K. Low-field magnetic relaxation M( t) data near H 2p/ H on indicates a distinct change of flux creep behavior. For H< H on, the relaxation mechanism follows the collective creep model M( t)= M 0[1+( μk B T/ U 0)ln( t/ t 0)] −1/ μ and crosses to the vortex glass model M( t)= M 0( t/ t 0) 1/[1−( Uo/ k B T)] when H> H on. Such a crossover behavior implies a change in vortex coupling mechanism from vortex quasi-lattice to entangled vortex glass.
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