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 (M,) value ranged from 9 to 38 emu g(-1). On heating, the crystallite size increased with corresponding increase in M-s values. At 1073 K all samples achieved M-s values close to 73 emu g(-1). On increasing the crystallite size, the coercivity (H-c) 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 M-s = 60 emu g(-1) and H-c = 1.42 kOe after thermal annealing at 973 K. The Mossbauer spectra were recorded for CoFe2O4 having a range of crystallite sizes at room temperature and at low temperatures down to 40K. The magnetic and Mossbauer results are provided for nanocrystalline CoFe2O4 as a function of crystallite size and measurement temperature. (C) 2001 Elsevier Science B.V. All rights reserved.