Temperature dependence of the magnetization of a Bi2Sr2CaCu2O8+ delta single crystal close to Tc.

The magnetization M(T,H) of a ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ single crystal has been measured above and below the superconducting transition temperature in externally applied magnetic fields H up to 50 kOe for H\ensuremath{\parallel}c. We find that M(T,H) is independent of H at a particular temperature ${\mathit{T}}^{\mathrm{*}}$ for external fields exceeding 10 Oe, and exhibits a two-dimensional (2D) scaling behavior as a function of [T-${\mathit{T}}_{\mathit{c}}$(H)]/(HT${)}^{1/2}$. The parameters ${\ensuremath{\xi}}_{\mathit{a}\mathit{b}}$(0)\ensuremath{\approxeq}21.4 \AA{} and ${\ensuremath{\xi}}_{\mathit{c}}$(0)\ensuremath{\approxeq}0.4 \AA{} are estimated from fitting the experimental data to a full Lawrence-Doniach model calculation of the fluctuation-induced magnetic susceptibility. From the same analysis, we obtain ${\mathit{dH}}_{\mathit{c}2}$/dT\ensuremath{\approxeq}-14 kOe/K in the range 5 kOeH50 kOe.