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Magnetic relaxation and flux creep in ceramic (Bi, Pb)-2223 HTSC

Physica C Superconductivity
Publication Date
DOI: 10.1016/0921-4534(91)90425-x


Abstract The magnetic relaxation of ceramic( Bi, Pb)-2223 ( T c = 107.2 K) has been studied in the temperature range 305-100 K and in fields up to μ 0 H = 1T. The relaxation of the magnetization at temperatures up to 80 K can be well described by a logarithmic time decay due to thermal activation of vortex lines. The activation energy U 0 obtained from the relaxation rate S= 1 M ( dM dln t ) in the single barrier height model exhibits a strong temperature. Both in applied fields and in the remanent state the activation energy increases with temperature ( U 0 = 20–50 meV at T = 4 K, U 0 = 250–400 meV at T ⋟ 60 K). The distribution of pinning barriers has been evaluated and exhibits a peak at U 0 ⋟ 20–30 meV in the remanent state and U 0 ⋟ 15–20 meV in an applied field of μ 0 H = 1 T. These small values explain the rapid drop of the remanency at T ≥ 25 K, the peak in the relaxation rate at T ⋟ 10 K and the increase of H c1 at T ≤ 25 K.

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