Effect of grain size on the Néel temperature of nanocrystalline nickel ferrite

Thermally induced changes of nanocrystalline NiFe2O4 spinel synthesized by sol–gel auto-ignition method are investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and magnetization measurements (VSM). The average grain size of NiFe2O4 increases from about 29 to 50 nm as the calcination temperature increases from 500 to 1000 °C. The IR spectra show the absorption bands corresponding to stretching vibrations of tetrahedral and octahedral bonds. The Néel temperature of NiFe2O4 for various grain sizes were determined by the direct measurement of magnetization.