Field dependence of magnetization and magnetic relaxation in (Bi,Pb)2Sr2CaCu2O8 crystals.

The hysteresis loops and magnetic relaxation in (Bi,Pb){sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} crystals were measured at fields up to 5.5 T. The relaxation rate {ital dM}/{ital d} ln{ital t} 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 {ital M} and {ital dM}/{ital d} ln{ital t} as a function of the field. These expressions were used to fit our experimental data of field-dependent magnetization and relaxation rate.