Magnetic properties of hematite α-Fe₂O₃ nanoparticles synthesized by sol-gel synthesis method: The influence of particle size and particle size distribution

Marin Tadic – Matjaz Panjan – Biljana Vucetic Tadic – Jelena Lazovic – Vesna Damnjanovic
– Martin Kopani – Lazar Kopanja

   Using the sol-gel method we synthesized hematite α-Fe₂O₃ nanoparticles in a silica matrix with 60 wt% of hematite. X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra of the sample demonstrate the formation of the α-Fe₂O₃ phase and amorphous silica. A transmission electron microscopy (TEM) measurements show that the sample consists of two particle size distributions of the hematite nanoparticles with average sizes around 10 nm and 20 nm, respectively. Magnetic properties of hematite nanoparticles were measured using a superconducting quantum interference device (SQUID). Investigation of the magnetic properties of hematite nanoparticles showed a divergence between field-cooled (FC) and zero-field-cooled (ZFC) magnetization curves and two maxima. The ZFC magnetization curves displayed a maximum at around T_B = 50 K (blocking temperature) and at T_M = 83 K (the Morin transition). The hysteresis loop measured at 5 K was symmetric around the origin, with the values of coercivity, remanent and saturation magnetization H_C10K = 810 Oe, M_r10K = 1.34 emu/g and M_S10K = 6.1 emu/g respectively. The absence of both coercivity H_{C300 K} = 0 and remanent magnetization (M_r300K = 0) in M(H) curve at 300 K reveals superparamagnetic behavior, which is desirable for application in biomedicine. The bimodal particle size distributions were used to describe observed magnetic properties of hematite nanoparticles. The size distribution directly influences the magnetic properties of the sample.

Keywords: iron oxide, hematite α-Fe₂O₃, sol-gel synthesis, superparamagnetism (SPION), Morin transition, particle size effects

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