Iron Nanoparticles Fabricated by High-Energy Ball Milling for Magnetic Hyperthermia

Iron nanoparticles (FeNPs) have been successfully prepared by high-energy ball milling in air for various milling times from 1 h to 32 h. Their structure, particle size, elemental composition, magnetic, and inductive heating properties were investigated by means of x-ray diffraction (XRD) analysis, field-emission scanning electron microscopy, energy-dispersive x-ray (EDX) spectroscopy, vibrating-sample magnetometry, and magnetic induction heating, respectively. XRD analysis showed that the average crystallite size decreased to 11 nm after 10 h of milling, then remained almost unchanged for longer milling times. Coexistence of iron (Fe) and iron oxide (FeO) phases was detected after 12 h of milling. EDX analysis also confirmed the occurrence of oxidation, which can be reconciled with the corresponding decrease and increase in saturation magnetization ( M s ) with milling time when exposed to oxygen and when annealed under H 2 ambient due to oxygen reduction. The time-dependent magnetic and inductive heating responses of the FeNPs were investigated for prospective application in magnetic hyperthermia. The effect of varying the alternating-current (AC) magnetic field strength on the saturation heating temperature and specific loss power of FeNP-containing ferrofluid with concentration of 4 mg/mL was also studied and is discussed.