Properties of carbon microspheres with magnetic graphite nanostructures

E. Sharoyan, A. Manukyan, A. Mirzakhanyan, C. Sanchez, A. Kocharian, O. Bernal
California State University. Los Angeles,
United States

Keywords: magnetization, susceptibility, graphite nanostructures

Summary:

In recent years, the carbon microspheres attract great attention due to applications in various areas, namely, in supercapacitors, filters of gases and fluids, fuel cells as substrates. Among practical applications is a high-temperature magnetism, observed in various carbon-based materials, etc. Below we present a number of preliminary results related to synthesis and investigation of carbon microspheres with interesting magnetic properties. Carbon microspheres have been prepared by using the method of solid-phase pyrolysis where as a precursor metal-free phthalocyanine was used, according to the reaction H2(C32H16N8) -> 32C. By changing the pyrolysis conditions we prepared carbon microspheres with a mean diameter 2-3.8 μm consisting of graphitized nanocrystallites with a thickness of 5-15 graphene layers and width of 5-20 nm and sufficiently narrow size distribution. In particular, at T_pyr=700°C and tpyr=60 min we obtained carbon microspheres with a mean diameter d=3.4±0.15 μm. Magnetic characteristics of these samples were investigated with a vibrational magnetometer in the temperature range 5-300К, in magnetic fields up to 80 kOe, as well as with the ESR method. Analysis of curves М-Т and М-Н presented shows the presence of paramagnetic centers with the concentration n=3∙10^19 spin/g and temperature-independent diamagnetism with susceptibility of χ_Dia=1.5∙10^-6 emu/g∙Oe. The parameters of ESR spectrum were measured at 300K: the g-factor 2.0031 and intensity ~5∙10^19 spin/g.