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

We studied the vortex pinning properties in Bi2.2-xPbxSr1.8CaCu2O8+y (0 less than or equal to x less than or equal to 0.6)single crystals, with and without laminar microstructures (LM's) parallel to the a axis. We found a large and temperature-dependent in-plane anisotropy in the critical current density (J(c)) in the case of x= 0.6 with LM's. Magnetization under various field 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 away from the LM's. This strongly supports that LM's act as planar pinning centers 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].