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

Abstract

We have studied the field-induced dimensional crossover in the fluctuation magnetization of three single crystals of Y Ba2Cu3O7−x, with superconducting transition temperatures, Tc= 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, M vsT , for temperatures close to the transition temperature Tc(H). The study was accomplished by obtaining isochamps magnetization curves as a function of temperature for fields in the range of 0.1 T to 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 Hcross, 3D-2D, with the content of oxygen in Y Ba2Cu3O7−x. It is observed that the evolution of the field Hcross 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. pacs74.40.+k

Onset of phase correlations inYBa2Cu3O7−xas determined from reversible-magnetization measurements

“…We mention that values of T c ͑H͒ obtained from this linear method produced consistent values of dH c2 / dT Ͻ 0 for all samples in reasonable agreement with the values listed in Ref. 13. Results for the fitted values of T a ͑H͒ and m are shown for different samples and field orientations in Figs.…”

“…This interesting feature occurs in two-dimensional ͑2D͒ systems [15][16][17] and in three-dimensional systems 17,18 and can be explained in terms of vortex fluctuations. The crossing point was previously investigated for the same deoxygenated samples studied here, 13 and will not be discussed further.…”

Magnetic phase diagram of the layered superconductor Bi2+xSr2−xCuO6+δ(Bi2201) withTc≈ 7 K

“…2), suggests absence of dimensional crossover induced by magnetic field, as observed in deoxygenated YBa 2 Cu 3 O 7−δ . [32,33] The results of Fig. 3 above, as well the similarity between M(T ) curves of Bi2201 and Bi2212 [15] evidences the 2D character of the studied system.…”

Onset of phase correlations in YBa2Cu3O{7-x} as determined from reversible magnetization measurements

“…This interesting feature occurs in 2D systems [15,16,17] as well in 3D systems [17,18], and can be explained in terms of vortex fluctuations. The crossing point was previously investigated for the same deoxygenated samples studied here [13], and it will not be discussed further.…”

“…The optimally doped Y Ba 2 Cu 3 O 7−x single crystal had a composition of x ∼ 0.05 with T c =91.7 K , and have approximate dimensions of 1x1x0.3 mm and mass ≃ 1.7mg . For the underdoped samples with H ĉ, we used magnetization data previously obtained from two deoxygenated crystals [13] with compositions of x = 0.5 and 0.6, and corresponding transitions at T c =41.5 and 52 K, respectively (these two samples have approximate dimensions of 1x1x0.2 mm and mass ≃ 1mg) . For the Nb sample, we used the magnetization data previously presented in Ref.…”