Determination of critical superconducting parameters based on the study of the magnetization fluctuations for RE3Ba5Cu8O18-δ (RE = Sm, Eu, Gd, Dy and Ho) ceramic superconductor system

In this paper, we report the production of cuprate-like superconductor RE3Ba5Cu8O18-delta (RE-358, RE = Dy, Gd, Sm, Eu and Ho) by using the solid reaction method. By means of vibrating sample magnetometry technique (VSM), magnetization curves as a function of temperature were acquired in a Zero Field Cooled/Field Cooled (ZFC/FC) mode. Critical temperature T-c and irreversibility temperature T-irr values were obtained from magnetization curves. The irreversibility line was constructed with T-irr data, it showed an Almeida-Thouless dominant trend for low magnetic fields and Gabay-Toulose behavior for high magnetic fields. Thermodynamic fluctuations were analyzed on magnetic measurements using Bulayskii, Ledvij y Kogan model (BKL) that analyze the vortex fluctuations on Lawrence-Doniach (LD) framework. With this model, penetration length parameters lambda(ab) and ab-plane coherence length xi(ab) band c-direction xi(c) was obtained. Crossing point coordinates of the excess magnetization vs. temperature curves for different applied magnetic field amplitudes T* and Delta M-ab* were determined. Weak magnetic fields were fitted at Delta chi/T limit as a function of reduced temperature epsilon (>= 10(-2)). This procedure allowed us to obtain the mid-field transition temperature value T-c0. Likewise, A(s) (Schmidt diamagnetism) and B-LD (LD parameter) constants were found for each of the RE-358 system samples. This showed that through thermodynamic fluctuations analysis, RE-358 system has an excellent bidimensional behavior (2D) and it is strongly anisotropic.