Elucidation of the stable vortex state across the peak effect region in CeRu₂

We present magnetization data on a weakly pinned single crystal of CeRu₂, showing the existence of a stable state of the vortex matter in the peak effect (PE) region. The stable state is achieved by cycling the magnetic field by a small amplitude. It is characterized by a unique value of the critical current density, independent of the magnetic history of the sample. The results support a recent phenomenological model proposed by Ravikumar et al. [Phys. Rev. B 61 (2000) R6479] which postulates a specific recipe to incorporate the history dependence of the current density. Our data also shows the occurrence of a first order phase transition from an ordered vortex phase to a disordered phase across the PE.