ac-Susceptibility study of critical current density in metal-substituted ErBa₂Cu₃O_7-δ

Abstract

Studies of the ac susceptibility of the pure ErBa₂Cu₃O_7-δ (Er-123) and the substituted samples ErBa₂ (Cu_0.995M_0.005)₃O_7-δ (M=Fe, Ni, Co, Ga) have been made at different ac field amplitudes. Analysis of the temperature dependence of the ac susceptibility at these fields [X-T plots] has been done employing Kim’s critical state model. The dopants are found to lower the temperature-dependent intergranular critical current density, J_c(T), of the Er-123 system at different rates. Fe doping decreases the J_c at the highest rate whereas Ni substitution results in the least rate of J_c lowering; the depression rates for Ga and Co doped samples are similar and intermediate. These results fully support the findings of our previous study [Phys. Rev. B 52, 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 system. The lower J_c of the Fe, Ni, Co, and Ga substituted samples is attributed to the reduction in the zero-temperature pinning potential I₀(0) brought about by the dopants.