Magnetic structure at γ-Fe2O3-organic interfaces

The effect of an organic coating on the magnetic properties of γ-Fe2O3particles has been studied using Mössbauer absorption, infrared absorption, and magnetization measurements; particular emphasis has been placed on the magnetic structure at the γ-Fe2O3- organic interfaces. Experiments were performed on fine γ-Fe2O3particles (≈ 300 Å) and also on conventional micron-size acicular γ-Fe2O3particles. The presence of a coating was confirmed by infrared-absorption spectra and by somewhat reduced saturation magnetizations. Although some increase in coercivity is observed for micron-size samples, the origin of this increase is suggested to lie in the change in packing factor when the nonmagentic organic materials are introduced. No substantial increase in coercivity is observed for coated fine particles. Mössbauer analyses have revealed that the surface magnetic structure of the pigment is unchanged by the organic coatings; neither a magnetically "dead" layer nor a pinned structure is formed. It appears that some effects reported for nonmagnetic coatings earlier may be secondary ones.