Evidence for planar pinning in heavily Pb-substituted Bi2Sr2CaCu2O8-gamma single crystals

We studied the vortex pinning properties in Bi2.2-xPbxSr1.8CaCu2O8+y (0 les s than or equal to x less than or equal to 0.6)single crystals, with and wi thout laminar microstructures (LM's) parallel to the a axis. We found a lar ge and temperature-dependent in-plane anisotropy in the critical current de nsity (J(c)) in the case of x= 0.6 with LM's. Magnetization under various f ield directions was measured using micro-Hall probes. J(c), when the field is tilted within the LM's, is larger than that when the field is tilted awa y from the LM's. This strongly supports that LM's act as planar pinning cen ters in this system. We also found a crossover from fishtail-like behavior to second-peak-like behavior when the field is tilted more than 70 degrees from the c axis. [S0163-1829(99)50938-7].