Synthesis and calcinations effects on size analysis of Co3O4 nanospheres and their superparamagnetic behaviors

• Spinel Co3O4 nanoparticles are synthesized by fast and effective microwave route.
• Tuning of size and morphology of Co3O4 was investigated by calcination temperatures.
• Well defined sphere morphology was achieved for the calcinations of 600 °C.
• The prepared Co3O4 was modified into moderate size of less than 20 nm for 600 °C.
• The 600 °C calcined sample completely obeys superparamagnetism nature from 5K–300K.

Co3O4 nanoparticles were synthesized by microwave process using citric acid as a capping agent. Interestingly, when calcination temperature is increased to 600 °C, nanoparticles were formed into nanospheres of about less than 20 nm observed from SEM images. The particles were aggregated into bigger size of about 65 nm when the calcination temperature was increased to 800 °C. The samples calcined at 400 °C and 800 °C show superparamagnetism above the blocking temperature and the existence of small ferromagnetism is observed when T