Well-dispersed, ultrasmall, superparamagnetic magnesium ferrite nanocrystallites with controlled hydrophilicity/hydrophobicity and high saturation magnetization

A facile approach was developed to create well-dispersed, ultrasmall superparamagnetic magnesium ferrite nanocrystallites with controlled hydrophilicity/hydrophobicity and high saturation magnetization by a room temperature precipitation reaction followed by a solvent thermal process at low temperature. The in situ NaCl "cage" which self-formed during the room temperature precipitation reaction confined the formation, crystallization, and growth of the magnesium ferrite nanocrystallites, resulting in an ultrasmall average particle size of ∼3.7 nm, while a high saturation magnetization comparable with that of the bulk MgFe₂O₄ material was achieved with a low Mg²⁺ content of ∼10%. The surfaces of these superparamagnetic magnesium ferrite nanocrystallites could be modified with oleic acid/citric acid ester coatings to have controlled hydrophobicity/ hydrophilicity to ensure their good dispersion in either nonaqueous or aqueous environments. This approach could be readily applied to other ferrite material systems and promises a wide range of technical applications.