Magnetic relaxation of four-CuO2-layer TlBa2Ca3Cu4O11+δ single crystals

Abstract Flux creep properties were investigated in four-CuO 2 -layer TlBa 2 Ca 3 Cu 4 O 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 1.7 Pb 0.3 Sr 2 CaCu 2 O 8 crystals.