THE ANOMALOUS MIXED-STATE OF THE C15 LAVES PHASE SUPERCONDUCTOR CERU2- A MAGNETIZATION STUDY

We present a detailed magnetization study of the anomalous (H, T) regi me of CeRu2. using these results as well as a comparative study Involv ing two other type-it superconductors (Bi-2212 and 1% Fe-Nb) showing p eak effects, we first show that a picture of dynamic crossover of pinn ing properties is inadequate to explain the anomalous behaviour in CeR u2. We then argue that a first-order phase transition can explain the observed behaviour and we provide experimental evidence of such a tran sition in CeRu2 consistent with the Clausius-Clapeyron relation. The a pplicability of existing theoretical models and the role of magnetism in the anomalous (H, T) regime are discussed.