1 a 2Magnetization Decay due to Vortex Phase Boundary Motion in BSCCO

We identify a new regime of decay of the irreversible magnetization in clean Bi2Sr2CaCu2O8 crystals, at induction values close to the “second peak field ” at which the bulk critical current density steeply increases. A time window is identified during which the decay of the induction is controlled by the slow propagation of the phase transformation front across the sample. The origin of the second magnetization peak (SMP) manifest in Bi2Sr2CaCu2O8 (BSCCO) crystals at low temperature is the object of major controversy. Recent investigations of the role of weak disorder have confirmed its close relation-ship with the first order phase transition (FOT) observed at higher temperatures. This has lead to a generic phase diagram of vortex matter [1– 4], in which the SMP is thought to correspond to a phase transition from an ordered Bragg-glass at low vortex density (low fields) to a disordered vortex solid (glass) at high fields. One of the key experiments in favor of a phase transition at th