THERMALLY ACTIVATED FLUX-CREEP IN K3C60 SINGLE-CRYSTALS

Long-term magnetic relaxation in the fullerene superconductor K3C60 wa s measured on crystalline samples in a wide range of temperatures and magnetic fields. A logarithmic M(t) dependence is observed on single c rystals with 100% shielding fraction. The relaxation rate at different magnetic fields increases progressively with temperature. The flux-cr eep activation energy is found to be in the range from 10 to 80 meV wi th a peak in its temperature dependence. From measurements on samples with nonperfect stoichiometry we show that inhomogeneities strongly af fect the relaxation process and may mask a logarithmic behavior.