Field dependence of magnetization and magnetic relaxation in (Bi,Pb)2Sr2CaCu2O8crystals

The hysteresis loops and magnetic relaxation in (Bi,Pb${)}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$ crystals were measured at fields up to 5.5 T. The relaxation rate dM/d lnt exhibits a strong field dependence in the temperature range 6–20 K. By expanding Bean’s model of the critical current density to include the field dependence of the flux-creep effect, we developed expressions for both M and dM/d lnt as a function of the field. These expressions were used to fit our experimental data of field-dependent magnetization and relaxation rate.