Nanosized Iron Oxide Particles Entrapped in Pseudo-Single Crystals of γ-Cyclodextrin

A new technique to produce very small magnetic nanoparticles of maghemite (γ-Fe2O3) is presented. The particles form and precipitate in the presence of the oligosaccharide γ-cyclodextrin and in the final product remain entrapped in tiny pseudo-single crystals of the organic host. Evidence of nanosized particles embedded in the organic crystal was obtained by HR-TEM studies that showed the occurrence of uniformly dispersed particles with average diameter of 18 Å. The resulting objects gave diffraction patterns with the same spacing as that of cyclodextrin crystals without iron. The magnetic properties were investigated by ZFC−FC magnetizations, hysteresis loops, and ac susceptibility measurements. The compound presents a complex magnetic behavior that deviates from that predicted on the basis of the classic single domain particle model. The deviation is ascribed to the complex properties of the surface, which, for such small sizes, plays the major role in determining the total magnetic behavior.