Observation of magnetic dead layers at the surface of iron oxide films

Depth profiles of the magnetization of sputtered films of Fe 3O4 and its oxidized form, γ-Fe2O 3, were obtained by the new polarized neutron reflection technique. We find that the magnetization of Fe3O4 is constant throughout the thickness (2600 Å) of the film except for a surface region about 25 Å deep corresponding to the surface roughness. In contrast the oxidized sample shows a magnetically dead layer ∼150 Å thick at the surface. X-ray and transmission electron microscopy studies give no evidence that the surface layers differ structurally from the bulk of the film, although there is the possibility of a highly defective surface region formed during the oxidation process.