Dimensional Crossover in the Fluctuation Magnetization in YBa2Cu3O7- x and its Evolution with the Content of Oxygen

We have studied the field-induced dimensional crossover in the fluctuation magnetization of three single crystals of YBa₂Cu₃O_7-x, with superconducting transition temperatures, T_c = 62.5, 52, and 41 K. The dimensional crossover is observed by studying the diamagnetic vortex fluctuations of the lowest-Landau-level type which occur in isochamps magnetization curves, MvsT, for temperatures close to the transition temperature T_c(H). The study was accomplished by obtaining isochamps magnetization curves as a function of temperature for fields in the range of 0.1–5 T. Magnetization curves for each sample when plotted together show two distinct well resolved crossing points, one formed by low field curves and located at a higher temperature than the other formed by high field curves. A lowest-Landau-level scaling analysis is applied to the curves forming the crossing points and it is verified that lower field curves obey the three-dimensional form of this scaling while the higher field curves obey the two-dimensional form. The results allow to observe the evolution of the dimensional crossover field H_cross, 3D–2D, with the content of oxygen in YBa₂Cu₃O_7-x. It is observed that the evolution of the field H_cross with the content of oxygen in each sample qualitatively agrees with theoretical predictions and allow us to estimate the ratio of the anisotropy among the studied samples.