A new method for study the mixed state of high-Tc superconductors by using the relaxation of resistivity

A new method to study the mixed state of high-T-c superconductors by the relaxation of resistivity R-ff(t) experiments is theoretically and experimentally discussed. The theoretical method about how to calculate the decayed magnetization current J(i)(R-ff(t)) and the effective pinning energy of flux lines U(R-ff(t), J(i)(t)) from R-ff(t) is discussed. Two equations about J(i)(R-ff(t)) and U(R-ff(t), J(i)(t)) are obtained by the two-kind-of-flux-creep model. R-ff(t) experiments are performed at various temperatures and magnetic fields. U-J data are calculated. Reasonable physical parameters are derived by fitting the U-J data with two U-J relation models. Experiments and the U-J relation models support the new method and the two-kind-of-flux-creep model. (C) 1997 Elsevier Science B.V.