Magnetization study of superconducting grains in Bi 2.1Sr 1.9CaCu 2O 8+δ

Abstract

The field dependence of DC magnetization was measured on a parallelepiped sample of superconducting Bi 2.1Sr 1.9CaCu 2O 8+δ at different temperatures below T c with a maximum applied field of 160 kA/m. The experimental intragranular magnetization extracted from the measured magnetization data was analysed in terms of the Kim critical state model together with the surface barrier modified equilibrium magnetization. Even though at low temperature ( T = 5 K) the experimental data could be explained by magnetization derived from the Kim model, the ‘Z’-shaped loops observed at higher temperatures could be explained only by taking into account the surface barrier modified equilibrium magnetization. Material-dependent parameters, such as critical current density as a function of field, fields for first flux entry ( H 1) and last flux exit ( H 2) and lower critical field ( H c1), were estimated. At higher temperatures, the contribution of equilibrium magnetization ( M eq) is found to be dominating compared to the bulk magnetization. The possible reason for the significant contribution of equilibrium magnetization in granular superconductors is discussed.