Magnetic After-Effects in Magnetite

The magnetic after-effect in magnetite (Fe3O4) was investigated as a function of the Fe2+ vacancy concentration in the temperature range between −269 and +90°C. A small after-effect below −150°C is supposed to be related to the Verwey transition. A large magnetic after-effect was observed between −20 and 70°C. Its amplitude increased with the concentration of Fe2+ vacancies. A detailed analysis reveals that this relaxation is composed of two simple Debye processes with the following activation parameters: Q1 = 0.82 eV, τ01 = 3 × 10−13 s; Q2 = 0.88 eV, τ02 = 3 × 10−13 s. Both processes are attributed to jumps of Fe ions into vacant sites in the Fe lattice leading to a reorientation of the symmetry axis of the trigonal vacancies. The two activation energies are attributed to different distributions of the Fe2+ and Fe3+ ions around the vacancy.