Magnetic response of a single-crystal thin film Bi2Sr2CaCu2Oy

To test the utility of the modified Kim-Anderson model for study of the magnetic response of ceramic superconductors, we measured ac complex susceptibilities χn = χn′-iχn″ (n = 1,2,3,5,7) of a single-crystal thin film Bi2Sr2CaCu2Oy, and attempted to simulate the results in the framework of this model. Analyses of χn have shown that generation of the higher-harmonics can be reproduced pretty well, where the material parameters k and B0, the surface barrier ΔH and the lower critical field Hc1 involved were used as the fitting parameters. From the even-n harmonic susceptibility χ2 which reflects the asymmetric nature of the magnetization curve, we found that the critical-current density Jc of the Bi2Sr2CaCu2Oy film depends sensitively on the local flux density Bi. This result is a provoking contrast to the Bi dependence of Jc for an YBa2Cu3Oy film.