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

High-field magnetization with external magnetic fields parallel to the c-axis has been measured in high-quality YBa2Cu4O8 single crystal. The fluctuation-induced magnetization above Tc 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 -dHc2/dT=1.2 T/K near Tc, penetration depth λab(0)=1943 Angstrom, and coherence length ξab(0)=21.7 Angstrom were extracted. copyright 1997 American Institute of Physics