Irreversibility fields and pinning parameters in Hg-1223 superconductors

The irreversibility field B i is analyzed using the flux creep theory based on a depinning mechanism caused by thermally activated flux creep. Near the critical temperature T c, the calculated B i depends on power of (1 - (T/T c)2). At low temperatures, however, the measured B i increases more rapidly than the power law. This deviation from the power law has been ascribed to a different pinning mechanism in low temperatures. AC and DC magnetizations in Ag-based composites of Ag x(HgBa1.9Bi0.1Ca2Cu3O8+δ)1-x (x = 0.1, 0.2, 0.3 and 0.4) superconductors were measured using a SQUID magnetometer and a PPMS susceptometer at temperature range 5-150 K under magnetic fields up to 14 T. The irreversibility fields B i are estimated from the peaks of imaginary parts of AC susceptibilities and shown to agree well with the numerical estimation of the original flux creep equation available in low temperatures. The magnetization characteristics are also successfully analyzed using the pinning parameters