Nonlinear effective activation energy and field dependence of the critical current density in HgBa2Ca2Cu3O8+δ

The effective activation energy of HgBa2Ca2Cu3O8+δ superconductor was extracted from the magnetic relaxation measurements below 30 K, and a power-law dependence on current density was found. We also obtained the effective activation energy from the whole magnetic hysteresis (M-H) loops plotted at constant field-sweep rate. The data sets for the M-H loops at different temperatures overlap each other, and all fall on the smooth Ueff(J,0) curve based solely on the magnetization relaxation measurements. This indicates that the field dependence of magnetic critical current density in high-temperature superconductors is determined by the flux creep via nonlinear effective activation energy at low temperatures