THE ANOMALOUS MIXED-STATE OF THE C15-LAVES PHASE SUPERCONDUCTOR CERU2- II - HISTORY DEPENDENCE IN FIELD-COOLED MAGNETIZATION HYSTERESIS

We report an unusual history dependence of the field-cooled magnetizat ion in and around the peak-effect regime of the superconducting mixed state of CeRu2. Such history effects in magnetization are shown to be absent in the peak-effect regime of the high-T-c superconductor Bi-221 2. Some qualitative similarities with and at the same time considerabl e quantitative differences from relatively old studies of the history dependence of the transport critical current density (J(c)) in single- crystal Nb and Nb3Ge and Mo3Si amorphous films are examined. Our work indicates that the peak effect in CeRu2 is probably due to a first-ord er phase transition unlike the peak effect in Bi-2212, and that the la tter could be due to a continuous or second-order phase transition. Di fferences in details of the history effects suggest that the origin of the peak effect in CeRu2 is likely to be different from those for the se hard type-II superconductors.