Abstract
The vortex dynamics of (Y, Nd)Ba2Cu3O7−δ ((Y, Nd)123) superconductors have been studied using magnetic relaxation measurements obtained at different sweep rates. The temperature dependence of the dynamic relaxation rate (Q) is found to be not vanishing at T = 0 K, and also showed well developed maxima becoming broader and tending to move to higher temperatures with decreasing magnetic field. At temperatures close to the critical temperature (Tc), Q(T) showed well-developed minima becoming deeper and tending to move to lower temperatures with increasing field. These minima appeared to occur approximately at the same reduced temperature position [ T/Tc] as that of oxygen-controlled-melt-grown (OCMG)-Nd(123) samples, thus providing further support for pinning similarities between both systems. Both the field dependence of the characteristic pinning energy [ Uc] and relaxation rate showed significant inconsistency with the collective pinning theory but full agreement with the results of [Perkins et al., Phys. Rev. B 54, 12551 (1996)].