HIGH-FIELD MAGNETIZATION SCALING RELATIONS FOR PURE AND NI-SUBSTITUTED SINGLE-CRYSTAL YBA2CU3O7

Several scaling relations are inferred from magnetization data taken in fields up to 20 T on single crystal YBa2Cu3-xNixO7 where 0 less-than-or-equal-to x less-than-or-equal-to 0.03. A Bean-like critical state exists in the samples at high fields (less-than-or-similar-to 20 T) and low temperatures (4.2 K) regardless of x. Strong systematics are also displayed in the temperature dependent data: it is found that beyond an applied field breakpoint, which itself scales with temperature as (1-T/T(c))3/2, all the scaled hysteresis loops decrease in a universal manner. This universal behavior of the normalized magnetization is well described as a hyperbolic function of the normalized applied field. A quantitative study of the dependence of the measured magnetization as a function of the sweep rate of the applied field is also presented. The measured magnetization is found to depend logarithmically on the sweep rate. The simplest diffusion models are inadequate to explain the data.