Pinning regimes in the vortex solid and crossover between them in single crystals of 2H-NbSe2

We report on the ac susceptibility and the dc magnetization response measurements in the B-dc parallel to ab orientation, in weakly pinned single crystals of 2H-NbSe2, We have found evidence for a crossover-like feature between different pinning regimes in the vortex solid that is not associated with the peak effect phenomenon. Instead this crossover feature is associated with novel history dependent response. Such behavior is contrary to a theoretically proposed scenario that the crossover between weak to strong pinning regimes in the vortex state is associated with the peak effect phenomenon. In the field (B)-temperature (T) phase diagram we trace the crossover boundary between the different pinning regimes in the vortex solid which differentiates its location from that of the peak effect phenomenon in these crystals. (C) 2007 Elsevier B.V. All rights reserved.