MAGNETIZATION RELAXATION IN YBA2CU3O7-DELTA

The time and field sweep rate dependencies of magnetization in high te mperature superconductors are derived from a combined view based on th e thermally activated flux creep. The tau(0) in the magnetization rela xation expression M=M(0)+M(1) ln(1+t/tau(0)) is a macroscopic quantity related primarily to the sample geometry and other experimental condi tions via the effective activation energy U(J(0)). This activation ene rgy provides an alternative interpretation to the nearly inverse propo rtionality of tau(0) to the field sweep rate. The values of tau(0), in the magnetization relaxation of single crystal YBa2Cu3O7-delta are co nsistent with the calculated ones. As the nonlinear U(J) is taken into account, the curvature in the \M\-ln t plot may change from negative to positive over a sufficiently long time window, and the magnetizatio n hysteresis M(H) depends on the field sweep rate H by const+A ln H+B ln(2) H, where A is slightly larger than M(1) and B>0. A discussion of the temperature dependency of the normalized flux creep rate is at th e conclusion of the article.