Structure and magnetic properties of carbon encapsulated Fe nanoparticles obtained by arc plasma and combustion synthesis

Carbon encapsulated Fe nanoparticles were obtained using two methods: arc plasma and combustion synthesis. These powders were characterized by the following methods: SQUID magnetization measurements, transmission electron microscopy (TEM) and Mössbauer spectroscopy. The last two methods showed that Fe nanoparticles, obtained by both techniques belong to metallic and/or carbide phases, and are partially encapsulated by graphitic carbon. The particles had 10-100 nm in diameter, and were covered by carbon 5-15 nm thick layers. The transmission Mössbauer spectra revealed two magnetic and two paramagnetic components. In the plasma samples the largest part of iron was contained in the carbide phase while in the combustion samples the bcc α-Fe encompassed most of iron. The combustion sample has much higher content of carbon, indicating that the Fe particles were not covered by graphite layer totally, and were dissolved in the etching process. The dominant portion of combustion samples was not vaporized, thus the iron phase solidified from the liquid. The plasma-arc samples were synthesized via dual mechanism: growth of nanocrystals from the vapor phase (carbide) and solidification of the liquid micro-droplets in the cold zone (α-Fe and γ-Fe).