MAGNETIZATION STUDY OF SUPERCONDUCTING GRAINS IN BI2.1SR1.9CACU2O8+DELTA

The field dependence of DC magnetization was measured on a parallelepi ped sample of superconducting Bi2.1Sr1.9CaCu2O8+delta at different tem peratures below T-c with a maximum applied field of 160 kA/m. The expe rimental intragranular magnetization extracted from the measured magne tization data was analysed in terms of the Kim critical state model to gether with the surface barrier modified equilibrium magnetization. Ev en 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 takin g 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 exi t (H-2) and lower critical field (H-c1), were estimated. At higher tem peratures, the contribution of equilibrium magnetization (M(eq)) is fo und to be dominating compared to the bulk magnetization. The possible reason for the significant contribution of equilibrium magnetization i n granular superconductors is discussed.