IRREVERSIBILITY LINE IN SUPERCONDUCTING HGBA2CUO4-CRYSTALS(DELTA SINGLE)

The vortex phase diagram in HgBa2CuO4+delta single crystals (T-c=95 K) is investigated using dc-magnetic measurements. The irreversibility m agnetic field H-irr(T) decreases exponentially in the temperature rang e 20 less than or equal to T less than or equal to 88 K. At Tapproxim ate to 88 K, the H-irr(T) curve changes slope abruptly and a new mecha nism controls the irreversibility up to T-c. Magnetization versus magn etic field measurements (H parallel to c) show a second peak (increase of the critical current) in the range 5 less than or equal to T less than or equal to 50 K. The overall picture resembles the phase diagram of the Bi2Sr2CaCu2O8+delta and YBa2Cu3O7 compounds if one considers t he anisotropy epsilon=(m/M)(1/2) of HgBa2CuO4+delta, which lies in bet ween the two others. [S0163-1829(98)00938-2].