AC-SUSCEPTIBILITY STUDY OF CRITICAL-CURRENT DENSITY IN METAL-SUBSTITUTED ERBA2CU3O7-DELTA

Studies of the ac susceptibility of the pure ErBa2Cu3O7-delta (Er-123) and the substituted samples ErBa2 (Cu(0.995)M(0.005))(3)O-7-delta (M= Fe, Ni, Co, Ga) have been made at different ac field amplitudes. Analy sis of the temperature dependence of the ac susceptibility at these fi elds [X-T plots] has been done employing Kim's critical state model. T he dopants are found to lower the temperature-dependent intergranular critical current density, J(c)(T), of the Er-123 system at different r ates. Fe doping decreases the J(c) at the highest rate whereas Ni subs titution results in the least rate of J(c) lowering; the depression ra tes for Ga and Co doped samples are similar and intermediate. These re sults fully support the findings of our previous study [Phys. Rev. B 5 2, 1320 (1995)] of the flux creep effects on the same batch of samples wherein it was observed that the concerned substituents had a similar effect on the flux creep activation energy values (E(a)) of the syste m. The lower J(c) of the Fe, Ni, Co, and Ga substituted samples is att ributed to the reduction in the zero-temperature pinning potential I-0 (O) brought about by the dopants.