VORTEX PHASE-DIAGRAM VIA MAGNETIZATION MEASUREMENTS FOR H-VERTICAL-BAR-VERTICAL-BAR-C IN BI2SR2CACU2O8

DC and AC magnetization for H parallel to c-axis of an air-annealed Bi2Sr2CaCu2O8 single crystal have been investigated in detail. In a DC magnetization (M-H) curve above 30 K a distinct kink has been observed at H-k close to the irreversibility field (H-irr), where a distinct change also in AC loss (chi '') has been observed. Below 40 K a prominent second peak has been exhibited in the M-H curve. It has been shown that the field (H-m) at the maximum \dM/dH\, where the second peak grows rapidly, is almost temperature independent. The chi '' versus H-DC curve has exhibited a sharp dip near the H-m. Also has been observed another characteristic field H-t where a crossover in the magnetic relaxation occurs. These characteristic fields (H-k, H-m and H-t) give a well defined vortex phase diagram, which is discussed in relation to a flux-melting and a possible vortex/Bose glass transition.