Hg-1223超伝導体の不可逆磁界とピンニングパラメータ(電気工学科)

Abstract

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 Hg-based composites of Ag_x(HgBa_<1.9>Bi_<0.1>Ca_2Cu_3O_<8+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 5-150K 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.