Critical Field Anisotropy of a Single Crystal GdBa2Cu3Ox and HoBa2Cu3Ox

Abstract
A study of anisotropic critical field has been carried out on single crystal samples of GdBa2Cu3O x and HoBa2Cu3O x . The angular dependence of the upper critical field can be fitted to the anisotropic Ginzburg-Landau model. The anisotropy ratio H c2 /H c2 // depends somewhat on the definition of H c2 and is also temperature dependent, but it generally falls between 3 and 7. The superconducting properties of GdBa2Cu3O x and HoBa2Cu3O x are almost identical with that of YBa2Cu3O x which we reported earlier, except for small differences in T c.