Evidence of ferromagnetic behaviour in carbon nanospheres synthesised by the chemical vapour deposition technique

The magnetic and electrical properties of two different sets of carbon nanospheres synthesised by chemical vapour deposition were investigated, using a state-of-the-art Physical Property Measurement System (PPMS). Scanning electron microscopy imaging of the carbon nanospheres revealed a difference in size with a diameters distribution of approximately 200-400 nm and 400-500 nm. PPMS magnetic measurements of the 400-500 nm diameter carbon nanospheres exhibited diamagnetism at high temperatures and clear superparamagnetic behaviour at very low temperatures (<10 K). However, ferromagnetism was observed in carbon nanospheres of diameter < 400 nm. The results obtained from both inductively Coupled Plasma Mass Spectrometry and Mossbauer spectroscopy, and as well as the calculated saturation magnetisation indicate that the observed ferromagnetism in the carbon nanospheres of diameter < 400 nm is intrinsic and could not be accounted for by the magnetic impurities such as Fe and Ni introduced during the synthesis process. The electrical properties of a network of carbon nanospheres were investigated and showed a variable range hopping class of conductivity.