Dissipative behavior and γ-irradiation of silver-sheathed Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_x tape

Dissipative mechanisms in Bi_1.8Pb_0.4Sr₂Ca₂Cu₃O_x tapes were investigated using magnetoresistance measurements and V-I characteristics. A considerable broadening of the resistive transition in applied magnetic field was observed up to a field of 0.5 T. The temperature and magnetic field dependence of the resistance R(T,B) were fitted to the Arrhenius relation and from which the magnetic field dependence of the pinning energy U₀(B) approx. B^-α with α ≈ 0.9 was derived. The variations of the critical current densities J_c with temperature and magnetic field before and after γ-irradiation were also studied. The temperature dependence of J_c(T) was fitted to the relation J_c(T) approx. (1 - T/T_c)ⁿ with n = 1.9 and discussed in terms of thermally activated flux flow (TAFF). However, J_c(B) results were explained based on the weak links, grain boundaries, and Josephson junctions in which it shows a power law behaviour J_c(B) approx. B^-0.5. At relatively low temperatures and magnetic fields, the critical current density was increased with a γ-irradiation up to a dose of 100 MR.