IRREVERSIBILITY LINE AND MAGNETIC-RELAXATION IN A SM1.85CE0.15CUO4-Y SINGLE-CRYSTAL

We report on the static and dynamic magnetic behavior of a Sm1.85Ce0.15CuO4-y single crystal for fields ranging from 20 Oe to 6 kOe. The irreversibility line, extracted from static magnetization versus temperature measurements in different magnetic fields H, shows power law behavior with an exponent that changes at approximately 1 kOe from 1.7. for fields H less-than-or-equal-to 1 kOe to 3.5 for H greater-than-or-equal-to 1 kOe. The magnetic relaxation study shows that for values of the applied field greater than 600 Oe, an extrapolation of the normalized relaxation rate S(n) to zero temperature gives a non-zero value. This may be indicative of nonthermally activated relaxation processes. For 1 kOe, S(n) versus temperature exhibits two peaks, a possible indication of the presence of two pinning mechanisms. A distribution of activation energies for the pinning barriers was inferred to explain the experimental observations. The distribution functions were calculated from magnetic relaxation data taken in different applied magnetic fields.