Manifestation of history-dependent critical currents via dc and ac magnetization measurements in single crystals of ${\mathrm{CeRu}}_2$ and $2H-{\mathrm{NbSe}}_2$

A study of path dependent effects in single crystals of ${\mathrm{CeRu}}_2$ and $2H-{\mathrm{NbSe}}_2$ shows that critical current density $J_c$ of the vortex state depends on its thermomagnetic history over a very large part of $\mathrm{}(H,T)\mathrm{}$ parameter space. The path dependence in $J_c$ is absent above the peak position (i.e., $H>\mathrm{}{H}_p)$ of the peak effect region, which we believe identifies the complete loss of order in the vortex structure. The highly disordered field cooled (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 field cooled state with sufficient ac field (few Oe).