Temperature dependence of irreversibility fields in Re doped Hg-1223 superconductors

Abstract Hg-based superconductors of HgBa 2 Ca 2 Cu 3 Re x O y ( x =0.15 denoted as Hg–Re0.15, x =0.18 as Hg–Re0.18 and x =0.2 as Hg–Re0.2) were fabricated by high vacuum sealing and sintering method using a precursor. Grain alignment was formed magnetically under external magnetic field of 10 T. AC susceptibilities and DC magnetizations were measured using a SQUID magnetometer and a PPMS susceptometer at temperature range 5–150 K under magnetic fields up to 14 T. The critical temperatures are 132 K for Hg–Re0.15, 130 K for Hg–Re0.18 and 133 K for Hg–Re0.2 determined by the temperature dependence of AC susceptibilities. The imaginary parts of AC susceptibilities show the double peak structure at low magnetic fields. This double peak structure is confirmed to suggest different depinning mechanisms. The irreversibility fields B irr estimated from the upper peaks of imaginary parts in Hg–Re0.18 sample for B ∥ ab are the largest. Theoretical analysis using the flux creep theory based on a depinning mechanism caused by thermally activated flux creep is favorably compared with the temperature dependence of B irr .