Phase Composition of Iron Oxide Nanoparticles Studied Using Hard X-ray Absorption Spectroscopy

At the surface ofiron oxide nanoparticles, an oxidizedor disorderedlayer is often found. Due to the large surface-to-volume ratio ofnanomaterials, such a surface layer plays an important role in theoverall magnetic properties of the particles. Consequently, it isimportant to characterize the surface layer if applications of ironoxide nanoparticles, e.g., for magnetic hyperthermia, magnetic particleimaging, or ferrofluidics, are envisaged. In this work, we tuned thephase of the surface layer of 14 nm iron oxide nanoparticles via annealingprocedures. The phase composition of the particles is systematicallystudied using hard X-ray absorption spectroscopy.