Abstract
Time-dependent decay of the magnetic moment and magnetization measurements were used to study pinning and flux creep in two samples with and without a j(B) maximum in nonzero field (fishtail effect). From both measurements the E(j) relation was reconstructed for B \\ c and the characteristic current exponent mu was obtained. At high j and low B mu values are between 1 and 4; with increasing B mu passes a maximum and approaches negative values. At low j mu is below 0.5 and not dependent on B or j. This behavior, which is qualitatively the same in both samples, is compared with proposed phase diagrams of the vortex lattice. Large mu values are correlated with the plateau of the normalized creep rate S almost-equal-to 0.025; both observations indicate low relaxation and are found in that low B region for which j(B) has its minimum. This observation rejects a dominating influence of relaxation on the fishtail effect.