Magnetic properties of nanocrystalline CoFe2O4 powders prepared at room temperature: variation with crystallite size

The magnetic properties of nanocrystalline CoFe2O4 powders prepared by a redox process at room temperature have been studied by vibrating sample magnetometer (VSM). The average crystallite size of the powders varied from 6 to 20 nm by changing the synthesis conditions and the corresponding saturation magnetisation (Ms) value ranged from 9 to 38 emu g−1. On heating, the crystallite size increased with corresponding increase in Ms values. At 1073 K all samples achieved Ms values close to 73 emu g−1. On increasing the crystallite size, the coercivity (Hc) increased passed through a maximum and dropped. Cobalt ferrite powder with an average crystallite size of 6 nm prepared at room temperature achieved desirable values of Ms=60 emu g−1 and Hc=1.42 kOe after thermal annealing at 973 K. The Mössbauer spectra were recorded for CoFe2O4 having a range of crystallite sizes at room temperature and at low temperatures down to 40 K. The magnetic and Mössbauer results are provided for nanocrystalline CoFe2O4 as a function of crystallite size and measurement temperature.