Dimensional crossover in the irreversibility line in (Bi, Pb)(2)Sr2Ca2Cu3O10

We report on magnetic measurements in the vicinity of the irreversibility l ine showing a field-induced dimensional crossover in the vortex ensemble in (Bi, Pb)(2)Sr2Ca2Cu3O10. The temperature dependence of the irreversibility line changes its behaviour at a crossover field, H-cross = 3.0 +/- 0.5 kOe , observed in both DC magnetization and AC susceptibility data, independent ly of the alternating held and frequency. This yields an estimate for the a nisotropy factor in (Bi, Pb)2223, gamma = 45 +/- 5. Magnetization fluctuati on analysis shows that the applicability limit of the 3D-XY scaling model c oincides with the change of behaviour in the IL, which provides further evi dence for a dimensionality change in the vortex fluctuations. The pinning p otential of the system also shows a change in its held dependence at the sa me crossover field.