ELECTROMAGNETIC PROPERTIES OF HIGH-TC SUPERCONDUCTORS - RELAXATION OF MAGNETIZATION

In an external magnetic field varying with time, the flux distribution inside a superconductor is generally composed of three regions: the thermally assisted flux flow (TF) region, the flux creep (FC) region and the flux flow (FF) region, and a considerably large part of the superconductor is occupied by the FC region. The contribution of the FC region to the magnetization is not very different from that of the FF region for a conventional superconductor, but becomes noticeably different for a high T(c) superconductor, especially at higher temperatures. In this case, even the initial sharp decrease of the magnetization during the relaxation experiment is subject to flux creep. From the theoretical expression for the relaxation of the magnetization derived by taking account of these facts, it is pointed out that the existing estimation method of the pinning potential for flux creep from the gradient of a logarithmic decay leads to a considerable underestimation.