The structure and phase composition of colloidal SPM Fe3O4 NPs

The structure and phase composition of colloidal SPM Fe3O4 NPs remains puzzling despite the availability of increasing amounts of structural information. Various spectroscopic measurements have shown that the structure of SPM Fe3O4 NPs can be described as a magnetite core with a thin overoxidized (Fe3+) surface shell, which is compositionally close to a maghemite polymorph (γ-Fe2O3).9a, Conversely, the putative Fe3O4@γ-Fe2O3 core−shell structure has not been observed by X-ray diffraction or electron microscopy studies, supporting smooth nonstoichiometric Fe3O4+δ formulation of magnetite NPs. This is most likely attributed to the topotactic oxidation of the Fe3O4 surface with the formation of solid solution Fe3O4−γ-Fe2O3. Unambiguous determination of the structure and phase composition of SPM Fe3O4 NPs is important because these parameters dramatically affect the Ms values. For instance, improved purity and crystallinity of colloidal SPM Fe3O4 NPs produced at elevated temperatures are believed to be responsible for their enhanced Ms (70−85 emu/g),7,9 thus both bulk and surface composition information may be pertinent for elucidating the structure−property relationships for NPs. The capping ligand is another surface-based factor thought to be capable of enhancing Ms. 7,16 A better understanding of how the structure and phase composition of Fe3O4 NPs depend on their synthesis is thus necessary for more precise control over their magnetic properties. A process of heating SPM NPs by magnetization reversal effects induced under exposure to an external oscillating magnetic field. For example, hyperthermia induced in SPM NPs can be used to locally heat and thus destroy cancer cells. The mechanism of magnetic hyperthermia is not fully understood, despite multiple previous theoretical and experimental studies. Rosensweig developed the first theoretical approach, in which the specific absorption rate (SAR) produced by hyperthermia in diluted SPM ferrofluids is attributed to Neel and Brown relaxation processes. At the same time, for ́ particles ≥25 nm in size, ferromagnetic or FiM heat release is ascribed to hysteresis losses.18 This separation of relaxation and hysteresis losses has been subsequently criticized by Carrey and co-workers, who proposed a more comprehensive theoretical framework that combined Stoner−Wohlfarth-based theories, linear response theories, and equilibrium functions, intending to explain the SAR produced by magnetic NPs of any size. Later, Vallejo-Fernandez and co-workers concluded that the susceptibility losses are negligible and the heat is mostly generated by hysteresis loss. If you are looking for high quality, high purity and cost-effective Fe3O4, or if you require the latest price of Fe3O4, please feel free to email contact mis-asia.