FLUX CREEP AND IRREVERSIBILITY IN ELECTRON-DOPED PR1.85TH0.15CUO4-Y

High-quality crystallites of Pr1.85Th0.15CuO4-y were prepared by a solid state reaction technique and aligned in epoxy by a magnetic field. Magnetic relaxation of the remanent moment was measured with field H parallel to the ab plane. We interpret our data with a thermally activated flux creep model, and show that the effective pinning energy U0 increases with increasing T between 2 and 15 K. We find that U0 is not strongly dependent on applied field. The crossover from reversible to irreversible magnetization was found to follow the power law H = H(0) (1-T/T(c))1.7. The value of U0 for H parallel to the ab plane is found to vary from approximately-8 to approximately-40 meV between 2 and 15 K, respectively. Compared to YBCO, pinning in the electron-doped system is rather weak.