Radiation-Induced Synthesis and Superparamagnetic Properties of Ferrite Fe[sub.3]O[sub.4] Nanoparticles

Ultra-small magnetic Fe[sub.3] O[sub.4] nanoparticles are successfully synthesized in basic solutions by using the radiolytic method of the partial reduction in Fe[sup.III] in the presence of poly-acrylate (PA), or by using the coprecipitation method of Fe[sup.III] and Fe[sup.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 m[sup.2] kg[sup.−1] of radiation-induced nanoparticles at 60 kGy is higher than Ms = 18.2 A m[sup.2] kg[sup.−1] for coprecipitated nanoparticles. Both values are compared with nanoparticles coated with other stabilizers in the literature.