Size Dependence of Magnetic and Optical Properties of Co3O4 Nanoparticles

The effect of particle size on the magnetic and optical properties of cobalt oxide Co3O4 has been investigated. Single phase Co3O4 nanopaxticles were synthesized by co-precipitation route and their structure was confirmed through X-ray diffraction analysis. The average crystallite sizes of the nanoparticles as determined from the X-ray diffraction were found to lie in the range of 13 to 59 nm. At room temperature these particles show paramagnetic response and the DC magnetic moment of the samples showed an increasing trend with increasing particle size. Both the antiferromagnetic Neel temperature T-N and the low temperature moment depict finite size effects in the AC susceptibility measurements. The optical absorption studies show that there are two direct band gaps in Co3O4, the main energy band gap and a sub-band located inside the main energy gap. The values of these energy band gaps for the 45 nm particles were determined to be 3.15 and 1.76 eV, respectively. The direct band gap in these particles clearly shows a blue shift with decreasing size attributable to the quantum confinement effect.