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

Abstract

The effective activation energy of HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+{delta}} 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 ({ital M}-{ital H}) loops plotted at constant field-sweep rate. The data sets for the {ital M}-{ital H} loops at different temperatures overlap each other, and all fall on the smooth {ital U}{sub eff}({ital 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.