Evidence for planar pinning in heavily pb-substituted (formula presented) single crystals

We studied the vortex pinning properties in (Formula presented) (Formula presented) 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 (Formula presented) in the case of (Formula presented) with LM’s. Magnetization under various field directions was measured using micro-Hall probes. (Formula presented) 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 (Formula presented) from the c axis. © 1999 The American Physical Society.