Temperature effects on magnetic properties of Fe3O4 nanoparticles synthesized by the sol-gel explosion-assisted method

Fe3O4 nanoparticles were successfully synthesized by the sol-gel explosion-assisted method. The phase composition of products with different ratios of dry gel and explosive agent (3:1, 6:1, 12:1) was studied. Highly pure, well-crystallized, spherical and monodispersed Fe3O4 3-20 nm nanoparticles were obtained at the 12:1 ratio. X-ray photoelectron spectroscopy characterization of the as-synthesized nanoparticles demonstrated consistency with stoichiometric Fe3O4 surface composition. Zero-field cooled and field cooled measurements at 200 Oe validate that the anisotropy energy is greater than thermal energy up to 300 K for the ∼10 nm samples. The Verwey transition (metal-insulator) of magnetite nanoparticles takes place at 128 K (Tv). The effects of different temperatures of 5 K, 128 K, and 300 K on magnetic behavior were studied in detail. The results show that hysteresis behavior weakens as the temperature increases. Saturation magnetization (Ms) of 86.2 emu/g is the highest at Tv. Initial susceptibility (χα) increases as a function of temperature, whereas coercivity (Hc) decreases.