Superconducting and magnetic properties of Gd substituted 2:2:2:3 Bismuth cuprates (Bi_1.7Pb_0.3Sr₂Ca_2–xGd_xCu₃O_y)

The Bi_1.7Pb_0.3Sr₂Ca_2−xGd_xCu₃O_y system is investigated for different concentrations of Gd. X‐ray diffraction, electrical resistance, ac susceptibility, and dc magnetization studies are performed to study the changes in the superconducting and magnetic properties. Substitution of dilute quantities of Gd³⁺ for Ca²⁺ is found to change drastically the superconducting properties of the system. X‐ray diffraction results reveal that the volume fraction of the high‐T_c 2223 phase that is present in samples without Gd³⁺ (x = 0) vanishes even for x = 0.01. The T_c onset obtained from χ'_ac versus T decreases from 109 to 74 K for x = 0 to 0.1, whereas the loss peak from χ″_ac versus T decreases from 108 to 56 K for x = 0 to 0.05. The same behaviour is noticed from resistance measurements. The dc susceptibility studies show that except for the x = 0 sample all other samples follow a Curie‐Weiss behaviour in the normal state with Curie‐Weiss temperature θ of the order of 20 K. The data obtained are compared with our earlier results on Sm³⁺ substituted Bi‐2223 superconductors. The results are explained on the basis of a possible variation of hole concentration with trivalent rare earth ion substitution and also on the basis of the magnetic nature of the substituted ions.