Mössbauer study of intermediate superparamagnetic relaxation of maghemite (γ-Fe₂O₃) nanoparticles

In the present work, we have synthesized and characterized magnetic nanoparticles of maghemite γ-Fe₂O₃ to study their structural and magnetic properties. For the preparation, magnetite precursor, were oxidized by adjusting the pH = 3.5 at about 80 °C in an acid medium, The mean size of the maghemite particles calculated from the X-ray diffractogram was around 5.7 nm. Mössbauer spectroscopy measurements at room temperature show their superparamagnetic behavior. Furhermore, Mössbauer measurements were carried out at 77 K and 4.2 K in order to find the typical hyperfine fields of the maghemite. Magnetite phase was not found. FC and ZFC magnetization curves measured at 500 Oe indicate a blocking temperature of 105.3 K. The magnetization measurements also show almost zero coercivity at RT. TEM images show nanoparticles with diameter smaller than 10 nm, which are in good agreement with the X-ray pattern and the fitting of the magnetization data.