Superconducting and magnetic properties of Gd substituted 2:2:2:3 Bismuth cuprates (Bi1.7Pb0.3Sr2Ca2–xGdxCu3Oy)

Abstract

The Bi1.7Pb0.3Sr2Ca2−xGdxCu3Oy 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-Tc 2223 phase that is present in samples without Gd3+ (x = 0) vanishes even for x = 0.01. The Tc 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.