THERMAL FLUCTUATION EFFECTS ON THE MAGNETIZATION ABOVE AND BELOW THE SUPERCONDUCTING TRANSITION IN BI2SR2CACU2O8 AND YBA2CU3O7-DELTA CRYSTALS IN THE WEAK MAGNETIC-FIELD LIMIT

We present detailed experimental data of the magnetization, M(ab)(T,H) , of Bi2Sr2CaCu2O8 and YBa2Cu3O7-delta crystals on both sides of the s uperconducting transition, for magnetic fields, H, applied perpendicul arly to the ab (CuO2) planes. The data are analyzed in terms of therma l fluctuations in the weak H limit: In the reversible mired state belo w the transition, by taking into account the vortex fluctuations, as f irst proposed by Bulaevskii, Ledvij and Kogan, which are much more imp ortant in the Bi-based compounds. Above the transition, by taking into account the order parameter amplitude fluctuations (OPF), through a g eneralization to multilayered superconductors of the Schmidt-like appr oach.