The nanoparticles exhibit some novel optical and magnetic properties, which are different from its bulk material. Cobalt oxide has been known as a semi-conductor compound of p type with a Spinel structure. Therefore, they are used as gas sensor and absorbent of solar energy. Furthermore, they are employed as an effective catalyzer in environmental clearing. In the thermal gradation method, carbonyl cobalt Co2(CO)8 is often used as a precursor, though cobalt carbonyl is very toxic and expensive. Magnetic compounds have been among interesting issues for human beings for over 4000 years. In large societies, magnetic compounds including computer disks, credit cards, speakers, coolers, automatic doors, and many other devices can be observed on a daily basis. The structure and morphology of as-prepared Co3O4 nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The TEM images showed that the product nanoparticles consisted of dispersive quasi- spherical particles with a narrow size distribution ranged from 5 to 15 nm and an average size around 10 nm. The magnetic measurements confirmed that the Co3O4 nanoparticles show a little ferromagnetic behavior which could be attributed to the uncompensated surface spins and finite size effects. The ferromagnetic order of the Co3O4 nanoparticles is raised with increasing the decomposition temperature.
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