Experimental observation of two-dimensional fluctuation magnetization in the vicinity of T-c for low values of the magnetic field in deoxygenated YBa2Cu3O7-x

We have measured isofield magnetization curves as a function of temperature in two single crystals of deoxygenated YBaCuO with T-c=52 and 41.5 K. Isofield magnetization curves were obtained for fields running from 0.05 to 4 kOe. The reversible region of the magnetization curves was analyzed in terms of a scaling proposed by Prange, but searching for the best exponent upsilon. The scaling analysis carried out for each data sample set with upsilon=0.669, which corresponds to the three-dimensional-xy exponent, did not produced a collapsing of curves when applied to M vs T curves data obtained for the lowest fields. The resulting analysis for the Y123 crystal with T-c=41.5 K, shows that lower field curves collapse over the entire reversible region following Prange's scaling with upsilon=1, suggesting a two-dimensional behavior. It is shown that the same data obeying Prange's scaling with upsilon=1 for crystal with T-c=41.5 K, as well as low field data for crystal with T-c=52 K, obey the known two-dimensional scaling law obtained in the lowest-Landau-level approximation.