Abstract
Flux creep properties were investigated in four-CuO 2-layer TlBa 2Ca 3Cu 4O 11+ δ crystals. The relaxation rates defined as dln M/dln t were studied as functions of temperature and magnetic field. A linear temperature dependence of the relaxation rate between 2 and about 30 K yielded a temperature-independent energy barrier. Above 30 K, a decrease of the relaxation rate with increasing temperature was found and the relaxation rate approached zero at the irreversibility line. Field-dependent relaxation rates indicated a linear field dependence for the sample in a partially-penetrated state and a logarithmic function of field in a fully-penetrated state. The relaxation data were compared with those of Bi 1.7Pb 0.3Sr 2CaCu 2O 8 crystals.
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