Magnetic After-Effect measurements have been made in the temperature range 4–600K on both high-purity and carbon-charged, polycrystalline cobalt and on single-crystal cobalt samples following electron-irradiation at 30K with 3 MeV electrons to a dose of 1023m−2. Attention has been focussed on the relaxation spectra following anneal above 300K. In all irradiated samples, a strong reduction in the amplitude of the relaxation spectrum in the range 250–400K occurs during anneal in this temperature range; this is attributed to the migration of the Stage III defect. In the high-purity material, no low-temperature relaxation processes evolve during this anneal. In contrast, in impurity-doped samples, low-temperature peaks evolve which are attributed to the reorientation of complexes formed by the migrating Stage III defect being trapped at interstitial carbon and at substitutional impurities.