Manifestation of history dependent critical currents via dc and ac magnetisation measurements in single crystals of CeRu2 and 2H-NbSe2

A study of path dependent effects in single crystals of CeRu2 and 2H-NbSe2 show that critical current density Jc of the vortex state depends on its thermomagnetic history over a very large part of (H,T) parameter space. The path dependence in Jc is absent above the peak position (i.e., H > Hp) of the peak effect region, which we believe identifies the complete loss of order in the vortex structure. The highly disordered FC state can be healed into a relatively ordered vortex lattice by subjecting it to a large enough change in dc field (few tens of Oe) or by shaking the FC state with sufficient ac field (few Oe).