Magnetization of the extreme type II superconductor YBa2Cu3O7 with k > 100

Magnetization measurements were performed on YBa2Cu3O7 in fields up to 8 T at temperatures close to the superconducting transition Tsub(c) = 93 K. The thermodynamic critical field Hsub(c) was determined from the area between the normal and the superconducting magnetization curves. The initial slope dHsub(c)/dT/Tsub(c) is 190 G/K, and the value of K is derived using the basic GLAG relations, leading to K approx. = 180. The extrapolated specific heat jump at Tsub(c) is ΔC/Tsub(c) approx. = 10 mJ/(K2mole-Cu), in good agreement with the specific heat measurement, or with the value deduced from the normal state susceptibility. No evidence for an exceptionally large coupling strength has been observed. (author)