Upper Critical Field and its Anisotropy of EuBa2Cu3O7-x and GdBa2Cu3O7-x Studied in Preferentially Oriented Pellets

Abstract
Upper critical field H c2 and its anisotropy are studied in disk samples of EuBa2Cu3O7-x and GdBa2Cu3O7-x . Preferentially oriented samples with c-axis perpendicular to the disk plane show anisotropic behavior of H c2 for midpoints and almost isotropic behavior for the offset field. The critical field slopes (-dH c2/dT) for offset field are 0.9∼1.1 T/K for both Eu-compound and Gd-compound. An analysis based on a model of a quasi-two-dimensional anisotropic superconductor suggests that the anisotropy factor ε is 0.16 for both materials. A degradation of the critical field values was observed in these materials in a shorter period of time after sintering than in the case of Y-, Ho- and Er-compounds.