LOW-FIELD AC-SUSCEPTIBILITY STUDY OF FLUX-CREEP IN METAL-SUBSTITUTED ERBA2CU3O7-DELTA

Low-field ac-susceptibility studies of pure ErBa2Cu3O7-delta and subst ituted samples of ErBa2(Cu(0.995)M(0.005))(3)O-7-delta (M=Fe, Co, Ni, Ga) have been carried out in the frequency range up to 1 kHz. The acti vation energy for flux creep in the case of the doped samples is consi derably lower than that for the undoped sample. The analysis of the re sults within the framework of Muller's model [Physica C 159, 717 (1989 ); 168, 585 (1990)] shows that the intergrain critical current density gets considerably suppressed by the dopants. Employing a SIS junction model it is argued that this can be attributed to the reduction in th e Fermi energy of the system due to the localization caused by the pre sence of the dopant atoms.