Temperature dependence of vortex flux pinning in polycrystalline YBa 2Cu 4O 8

Abstract

Magnetization measurements versus the magnetic field were done on a polycrystalline YBa 2Cu 4O 8 sample over temperature range from 4.2 K up to T C = 80 K. Within the applicability of the Bean critical state model, the magnetization remanence Δ M R represents the pinning forces at H = 0. We found that Δ M R decreases sharply with the temperature T for T/ T C < 0.4 and for T/ T C > 0.4 square root behavior exists. We found that Δ M R scales according to the empirical formula Δ M R (emu/cm 3) = 13(1 − T/ T C) 6 + 2(1 − T/ T C) 1/2. The two distinct behavior of Δ M R with T implies an existence of different pinning mechanisms.