FLUX-CREEP DETERMINATION OF FIELD-DEPENDENCE OF MAGNETIC J(C), AT LOW-TEMPERATURES

The effective activation energy of one HgBaCaCoO 1223 superconductor a s a function of current density was extracted from the magnetic relaxa tion measurements below 30 K, and found to obey a power law. We also o btained effective activation energy as a function of current density f rom the magnetic hysteresis loops (M-H). The data sets for the M-H loo ps at different temperatures overlap each other, and all fall on the s mooth U-eff(J,O) curve based solely on the magnetization relaxation me asurements. This indicates that the field dependence of magnetic criti cal current density is determined by the flux creep via nonlinear effe ctive activation energy at loop temperatures.