Equivalence of dynamical and conventional magnetic relaxation in high-T-c superconductors

Measurements of the sweep rate dependence of the magnetic moment U of the high-T-c superconductor Bi2Sr2CaCu2O8 are shown to provide essentially the same information about the current dependence dU/dj of the activation energy U(j) as measurements of the time decay of U. However, at very short times the conventional relaxation rate R = -d In U/d In t is suppressed due to the existence of a waiting time tau(i) and needs to be replaced by measurements of U at various sweep rates dB(c)/dt. For a sufficiently strong relaxation process, the magnetic moment decays non-logarithmically in time. This is caused by the non-linear current dependence of the activation energy. Therefore, it is necessary to evaluate the conventional relaxation rate R and the dynamical relaxation rate Q = d In u/d In(dB(c)/dt) at the same value of the current density. It is shown that the conventional and dynamical relaxation rates are in good agreement with each other in a wide range of temperature and magnetic field.