Experimental observation of two-dimensional fluctuation magnetization in the vicinity of T_c for low values of the magnetic field in deoxygenated YBa_2Cu_3O_{7-x}

摘要

We measured isofield magnetization curves as a function of temperature in twosingle crystal of deoxygenated YBaCuO with T_c = 52 and 41.5 K. Isofield MvsTwere obtained for fields running from 0.05 to 4 kOe. The reversible region ofthe magnetization curves was analyzed in terms of a scaling proposed by Prange,but searching for the best exponent $\upsilon$. The scaling analysis carriedout for each data sample set with $\upsilon$=0.669, which corresponds to the3D-xy exponent, did not produced a collapsing of curves when applied to MvsTcurves data obtained for the lowest fields. The resulting analysis for the Y123crystal with T_c = 41.5 K, shows that lower field curves collapse over theentire reversible region following the Prange's scaling with $\upsilon$=1,suggesting a two-dimensional behavior. It is shown that the same data obeyingthe Prange's scaling with $\upsilon$=1 for crystal with T_c = 41.5 K, as welllow field data for crystal with $T_c$ = 52 K, obey the known two-dimensionalscaling law obtained in the lowest-Landau-level approximation.