The irreversibility field Hirr and the anomalous second peak in the magnetization curves have been studied from the magnetization measurements (H ∥ c-axis) for Pb2Sr2Y1-xCaxCu3O 8 single crystals with 0 ≦ x ≦ 0.5 and with the anisotropic parameter γ = (m*c/m*ab)1/2 of 24 ≧ γ ≧ 5. The temperature dependence of Hirr is discussed in terms of flux creep and 2D or 3D vortex-lattice melting. The anomalous second peak is observed for all x values. The peak shape is similar to that of YBa2Cu3O7-δ. The peak field Hp is dependent on temperature and proportional to (1 - T/Tc)3/2 near Tc. Both Hirr and Hp at each reduced temperature are proportional to γ-2. The origin of the second peak is discussed in terms of dimensional crossover of the vortices from 3D to 2D and collective pinning.
ASJC Scopus subject areas