CRITICAL FIELDS AND VORTEX STRUCTURE OF YBA2CU3O7-DELTA DERIVED FROM REVERSIBLE MAGNETIZATION

The magnetic-field and temperature dependence of the Ginzburg-Landau order parameter [f] is derived from magnetization studies for grain-aligned YBa2Cu3O7-delta in the region of thermodynamic reversibility, based on the Hao-Clem model. The value of [f] at 5 T and 89 K is still 52.3% of the zero-field value. Fitting the magnetization data to the Hao-Clem theory reveals that kappa(c) is a slowly decreasing function of temperature near T(c). H(c)(T) and H(c2)(T) were determined with high precision along with the kappa(c)(T) values. The detailed shape of the order parameter is derived from kappa(c)(T) and H(c)(T) data. Characteristic variables derived from the data are H(c)(0) = 1.18 x 10(4) Oe, lambda(ab)(0) = 1.31 X 10(3) angstrom, and xi(ab)(0) = 18 angstrom. The BCS fitting of H(c) reveals that the value of -dH(c2)/dT decreases from 2.25 T/K at T=82 K to 1.9 T/K at T(c) of 92.4 K.