Ferromagnetism of Nanographite Structures in Carbon Microspheres

Carbon microspheres with unusual magnetic properties have been prepared by the method of solid-phase pyrolysis where metal-free phthalocyanine was used as a precursor. The morphology, structure, and magnetic properties of prepared samples were investigated using electron microscopy, magnetometry, and electron paramagnetic resonance. Carbon microspheres with a mean diameter d = 3.40 ± 0.15 μm consist of graphitized nanocrystallites with a thickness of 5-15 graphene layers. The samples demonstrate a strong paramagnetism with the concentration of paramagnetic centers ~5×10 19 spin/g. In the temperature range of 5-100 K, a ferromagnetism was revealed with a maximum value of the saturation magnetization, M s ~ 0.03 emu/g at T = 25 K. The temperature-independent diamagnetism with susceptibility of χ Dia = -1 × 10 -6 emu/g · Oe was also measured.