Observation of iron diffusion in the near-surface region of magnetite at 470 K

Abstract

Experiments are reported, which allow us to quantify the near-surface cation diffusion in (001) oriented Fe3O4 single crystals at temperatures between 470 and 770 K. Thin homoepitaxial films of magnetite, grown using isotopically labeled Fe57, were investigated by neutron reflectivity and time-of-flight secondary ion mass spectrometry. By heating the thin films in high vacuum to different temperatures for a well-defined time and determining the Fe57 distribution along the surface normal, the diffusion lengths are obtained. For the investigated temperature range, diffusion constants of the order of 10-20 m2/s are deduced. These results are important in view of near-surface mass transport induced by oxygen chemical potential differences occurring when magnetite is exposed to different gas atmospheres or by adsorbates.