Synthesis of air-stable iron-iron carbide nanocrystalline particles showing very high saturation magnetization

Summary form only given. The authors have prepared coated iron nanoparticles which are air-stable by the sonochemical decomposition of Fe(CO)/sub 5/ in diphenylmethane (DPhM). The as-prepared material is superparamagnetic (M=88 emu/g at 15 kGs external field), confirming that the iron particle size is less than 10 nm, according to the published data. Air-stable dark gray magnetic powder is formed after annealing. The Mossbauer spectrum (MS) reveals that the annealed sample contains bcc Fe, iron carbide Fe/sub 3/C, and small amounts of Fe/sub 2/O/sub 3/ (/spl sim/3 at.%). The annealed material is ferromagnetic. The saturation magnetization, M/sub s/ and coercive force, H/sub c/, are equal to 212 emu/g and 40 Oe, respectively. The high resolution TEM picture shows that iron particles are covered by a crystalline shell with a thickness of about 3 nm. The shell does not exhibit the layered structure typical for graphite. It can be assumed that the coat consists of Fe/sub 3/C or a mixture of Fe/sub 3/C and C.