pinning force density in polycrystalline Bi₁.₈Pb₀.₄Sr₂Ca₂₋ₓYₓCu₃Oy multiphase systems

• Published in: Current applied physics Vol. 11; no. 4; pp. 1010 - 1014
• Main Authors: Mihalache, V, Deac, I.G, Pop, A.V, Miu, L
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-01-2011
• Subjects: Carrier density; Density; Doping; magnetic fields; Mathematical models; Pinning; Superconductivity; Superconductors; temperature; Yttrium
• ISSN: 1567-1739; 1878-1675
• DOI: 10.1016/j.cap.2011.01.015

ac susceptibility measurements as a function of temperature T and the ac magnetic field amplitude, Hₐc, have been performed on five superconducting Bi₁.₈Pb₀.₄Sr₂Ca₂₋ₓYₓCu₃Oₓ polycrystalline samples (x = 0, 0.005, 0.04, 0.15 and 0.36, and with the volume fraction of the Bi₂Sr₂Ca₂Cu₃Oy (2223) phase, f ≈ 100%, 100%, 64%, 0% and 0%, respectively. By using the Müller model for granular superconductors, we found that the pinning force density obtained from the imaginary peak of χ″(T) is strongly dependent on the doping level. To describe this dependence we adopted the multilayer model (a stack of superconducting, S, and normal, N, layers) of a superconductor. In the framework of this model, we demonstrated that (a) the yttrium addition influences the degree of coupling between the adjacent S layers (and thereby, the pinning strength) through the modification of the carrier concentration and of the effective thickness of the N layers, and (b) the intergrowth of Bi₂Sr₂CaCu₂Oδ (2212) layers within the 2223 grains has an important influence on the thickness of N.