We have measured the relaxation of the magnetic moment m in melt-textured YBa2Cu3O7-δ samples as functions of temperature and magnetic field from 10-4 to 330 s just below the irreversibility line. Inside this short-time window, the moment decays more than one order of magnitude and the time dependence of this decay can be described by m[ln(t/teff)]1/μ with the exponent μ∼0.3±0.05. As the vortex-glass temperature Tg is approached from below, we observed a sharp increase of the characteristic time teff. The scaled time teffT-Tgzν remains constant over a wide temperature range. As a result, the scaled moment m/T-Tg2ν versus the scaled time tT-Tgzν for different temperatures collapses over a broad logarithmic time window. The exponents are estimated to be zν=7.9 and ν=1.9. All these results can be explained quite satisfactorily within the framework of the vortex-glass model.
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