γ-Fe2O3 by sol–gel with large nanoparticles size for magnetic hyperthermia application

• Iron oxides nanoparticles with different sizes are successfully synthesized using sol–gel method.
• The obtained nanoparticles are mainly composed of maghemite phase (γ-Fe2O3).
• A non-negligible coercive field suggests that the particles are ferromagnetic.
• A mean heating efficiency of 30 W/g is obtained for the smallest particles at 110 kHz and 190 Oe.

Iron oxides nanoparticles with different sizes are successfully synthesized using sol–gel method. X-ray diffraction (XRD) and Mössbauer spectroscopy show that the obtained nanoparticles are mainly composed of maghemite phase (γ-Fe2O3). XRD and transmission electron microscopy (TEM) results suggest that the nanoparticles have sizes ranging from 14 to 30 nm, which are indeed confirmed by large magnetic saturation and high blocking temperature. At room temperature, the observation of a non-negligible coercive field suggests that the particles are ferro/ferrimagnetic. The specific absorption rate (SAR) under an alternating magnetic field is investigated as a function of size, frequency and amplitude of the applied magnetic field. A mean heating efficiency of 30 W/g is obtained for the smallest particles at 110 kHz and 190 Oe, whereas further increase of particle size does not improve significantly the heating efficiency.