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Description
Magnetite (Fe3O4) nanoparticles (NPs) coated with organic material are of considerable interest in many biomedical applications, such as magnetic resonance imaging, drug administration, magneto-impedance tumor detection, magnetic hyperthermia, among others. Additionally, these nanostructured systems experience changes in their magnetic properties due to the reduced size, crystallite shape, coating quality, as well as particle-particle interactions. Besides that, the mechanisms are not well understood yet. This work reports the effects of surface properties and particle-particle interaction on the magnetic properties of magnetite nanoparticles coated with oleic acid (Fe3O4@OA). The Fe3O4@OA NPs with three different sizes were prepared by a thermal decomposition method. X-ray diffraction and transmission electron microscopy revealed that the NPs have good crystallinity and almost spherical and polyhedral shapes. Infrared spectroscopy indicated that OA molecules are bound to the NPs surfaces via bidentate bonds (chelating and/or bridging). Likewise, the thermogravimetric analysis confirmed the presence of weakly and strongly bond OA molecules and allowed to quantify the NPs surface coating efficiency. On the other hand, magnetization curves are consistent with a core/shell structure formed likely by magnetite/maghemite phases, and the probable coexistence of iron ions in low- and high-spin states at the surface (shell) was evidenced. The magnetic characterizations show that, depending on the OA coating quality, it is possible to control the particle-particle separation distance, thus reducing particle agglomeration and, consequently, particle-particle interactions.
