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 (T
), 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/T
] 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
] 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)].