Reduction of the magnetization decay rate in high-Tc superconductors.

Abstract

Small decrements in the temperature \ensuremath{\Delta}T of superconducting samples in the critical state are shown to cause substantial reduction in the rate of magnetic relaxation. Quantitative agreement is obtained between experimental data and a model, which assumes the decay of the supercurrent subsequent to the change in temperature can be described in terms of the critical state. Experiments were performed in an applied field of 5.07 kG, on thick film (1.6 \ensuremath{\mu}m) samples which generate a substantial self-field (\ensuremath{\sim}5 kG). The effect of temperature reduction is shown to be calculable from a knowledge of the decay-rate exponent n and ${\mathit{J}}_{\mathit{c}}$(T) in the relevant temperature range. These results indicate that cooling in the critical state can be used to study magnetization decay at current densities reduced from the critical current.