Hg系超伝導体の交流帯磁率(電気工学科,工学部創設40周年記念号)

Abstract

Compounds of Ag_<0.1>(HgBa_<1.9>Bi_<0.1>Ca_2Cu_3O_<8+δ>)_<0.9> (Ag-01) and HgBa_2Ca_2Cu_3Re_<0.18>O_x (Hg-Re0.18) were fabricated by direct synthesis from the oxide powders and by high vacuum sealing and sintering method using a precursor, respectively. For Hg-Re0.18 sample, 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 131 and 130 K for Ag-01 and Hg-ReO.18, respectively, determined by the temperature dependence of DC magnetizations. Irreversibility fields B-1TT were estimated from the imaginary parts of AC susceptibilities. The double peak structure of Hg-ReO.18 sample in the imaginary parts is confirmed to suggest different depinning mechanisms. Hg-ReO.18 sample exhibits larger B_<irr> values, in particular at high temperatures, compared with Ag-01 sample. B_<irr> is determined by several factors, of which Re doping is favorable in enhancing the flux pinning properties. The temperature dependence of irreversibility fields is also explained well by the flux creep theory.