Two-dimensional fluctuations in the magnetization of the high-temperature superconductor LaBaCaCu3O7-delta

We report measurements of magnetization and diamagnetic susceptibility in p olycrystalline LaBaCaCu3O(7) (-delta) in high magnetic fields (20-50 kOe). The sample has a zero-field transition temperature T-co = 77 K and a transi tion width of 2.0K. The results show large fluctuation effects, which can b e explained by Ginzburg-Landau fluctuation theory for a two-dimensional sys tem. Using a theoretical model based on the lowest Landau-levels approximat ion. the magnetization data are fitted with good agreement. The weak-field fluctuation diamagnetic susceptibility above T-c can be fitted well in term s of the 2D Lawrence-Doniach model. (C) 2001 Elsevier Science B.V. All righ ts reserved.