Magnetic properties evolution of the CoxFe3-xO4/SiO2 system due to advanced thermal treatment at 700 °C and 1000 °C

• CoxFe3−xO4 (x=0.5–2.5) system embedded in the silica matrix was synthesised.
• The CoFe2O4 was obtained as single magnetic phase.
• The saturation magnetization decrease with the increase of the Co/Fe ratio.
• Magnetization increase and coercive field decrease with the calcination temperature.
• The CoFe2O4 crystallite size increase from 5–10.3 nm (700 °C) to 9–34 nm (1000 °C).

The CoxFe3−xO4 (x=0.5–2.5) system embedded in the silica matrix was synthesised by sol–gel method using cobalt nitrate, iron nitrate, 1.4-butanediol and tetraethyl orthosilicate. Five different Co/Fe molar ratios in the presence of diol and one without diol were used for the synthesis. The obtained gels were subjected to thermal treatment at 700 °C and 1000 °C. The oxide species formed in the silica matrix, the optimum temperature for the CoFe2O4 phase formation, the evolution of nanocrystallites size and magnetic properties with the calcination temperature were studied. The formed oxide species were studied using X-ray diffraction, Fourier transformed infrared spectrometry, the Co/Fe molar ratio was confirmed using inductively coupled plasma optical emission spectrometry, the nanocrystallites size, shape and clustering was identified by transmission electron microscopy and scanning electron microscopy, while the formation of magnetic phases was investigated by hysteresis and magnetization derivatives measurements.