Saturation magnetization change with structure in CoFe2O4 nanostructures prepared from metallic iron and cobalt by wet grinding method

Nanocrystalline cobalt ferrite (CoFe2O4) has been synthesized directly from metallic cobalt (Co) and iron (Fe) via wet-milling followed by calcination. The calcination took place in atmosphere at 750 ◦C. After calcination, samples were dry-milled for up to 12 h to investigate the effects of their mean crystallite sizes and microstress on their magnetic properties. The mean crystallite sizes of the samples were calculated from X-ray powder diffraction (XRD) patterns using a Rietveld analysis program (MaudLab). Results show that the calcined sample had a crystallite size of around 60 nm, which decreased to 12 nm after 12 h of drymilling. However, agglomerated nanocrystallites were observed in the transmission electron microscopy (TEM) images of the material. Rietveld analysis also shows an increase in microstrain from 2 x 10-4 to 1.4 x 10-3 after increasing the dry-milling time to 12 h due to crystal defects induced by collisions while drymilling. The electron binding energies of the Co+2 were measured by X-ray photoelectron spectroscopy (XPS) to determine the degree of inversion, which was used to calculate the saturation magnetization. Vibrating sample magnetometer (VSM) measurements revealed that milling decreased the saturation magnetization from 125 emu g-1 to 57 emu g-1 even the calculated saturation magnetization increased from 4.87 µB to 6.17 µB.