“Irreversibility Line” and magnetic relaxation in a Sm 1.85Ce 0.15CuO 4−y single crystal

Abstract

We report on the static and dynamic magnetic behavior of a Sm 1.85Ce 0.15CuO 4− 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 ∼ 1 koe from 1.7 for fields H⩽1 kOe to 3.5 for H⩾ 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. Thismay 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.