Thermodynamic properties of YBa2Cu4O8 crystal near upper critical fields Hc2(T)

Abstract
High-field magnetization with external magnetic fields parallel to the c -axis has been measured in high-quality YBa 2 Cu 4 O 8 single crystal. The fluctuation-induced magnetization above T c and a crossover of magnetization curves M(T) at T *=77.4 K were clearly observed for various magnetic fields, and analyzed by the high-field scaling law and the vortex fluctuation theory for three-dimensional systems. In the reversible temperature region, the magnetization is well described by the model of Hao et al. [Phys. Rev. B 43, 2884 (1991)]. From this analysis, the thermodynamic parameters such as upper critical field slope − dH c2 /dT=1.2 T/K near T c , penetration depth λ ab (0)=1943 Å, and coherence length ξ ab (0)=21.7 Å were extracted.