Radiation-Induced Synthesis and Superparamagnetic Properties of Ferrite Fe₃O₄ Nanoparticles

Ultra-small magnetic Fe₃O₄ nanoparticles are successfully synthesized in basic solutions by using the radiolytic method of the partial reduction in Fe^III in the presence of poly-acrylate (PA), or by using the coprecipitation method of Fe^III and Fe^II salts in the presence of PA. The optical, structural, and magnetic properties of the nanoparticles were examined using UV-Vis absorption spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and SQUID magnetization measurements. The HRTEM and XRD analysis confirmed the formation of ultra-small magnetite nanoparticles in a spinel structure, with a smaller size for radiation-induced particles coated by PA (5.2 nm) than for coprecipitated PA-coated nanoparticles (11 nm). From magnetization measurements, it is shown that the nanoparticles are superparamagnetic at room temperature. The magnetization saturation value Ms = 50.1 A m² kg^-1 of radiation-induced nanoparticles at 60 kGy is higher than Ms = 18.2 A m² kg^-1 for coprecipitated nanoparticles. Both values are compared with nanoparticles coated with other stabilizers in the literature.