Effect of Lower Critical Fields on Magnetization of a Single-Crystal Bi₂Sr₂CaCu₂O_8+d Bulk Superconductor

Abstract

To test the utility of the modified Kim-Anderson critical-state model for study of the magnetic response of ceramic superconductors, we measured the initial magnetization, hysteresis loops and ac complex susceptibilities X_n=X'_n-iX"_n(n =1, 2, 3, 5) of a single-crystal Bi₂Sr₂CaCu₂O_8+d bulk sample. The results were simulated in the framework of the model. Analyses of Xn have shown that generation of the higher harmonics can be qualitatively reproduced, where the material parameters k and B₀, surface barriers ΔH and lower critical fields Hcl, involved were used as fitting parameters. Comparison of the observed data with the calculated results has revealed that nonzero values of H_cl, play an essential role in the magnetic characteristics of the sample.