Influences of Surface Iron Oxide Layer on Magnetic Properties of Iron Pigment

Mössbauer spectroscopy and other methods were used to study the oxide layer on the surface of fine Fe particles. On the basis of X-ray and electron diffraction, the surface oxide phase was characterized as consisting of extremely fine spinel crystals of Fe3O4 and ¿-Fe2O3, and mixtures of these. Comparisons of the Mössbauer spectra under strong magnetic fields (25 and 50 kOe) of different samples indicated that the surface oxide layer is magnetized hardly at all, and the internal field in this layer is as much as 30 to 50 kOe lower than in the Fe material. While the local magnetic properties are those of a spinel phase, the oxide layer contributes hardly at all to the Fe particle magnetic properties.