Magnetic properties of nanocrystalline CoFe 2O 4 powders prepared at room temperature: variation with crystallite size

Abstract

The magnetic properties of nanocrystalline CoFe 2O 4 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 s) 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 Mössbauer spectra were recorded for CoFe 2O 4 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 CoFe 2O 4 as a function of crystallite size and measurement temperature.