Magnetic properties of carbon‐coated, ferromagnetic nanoparticles produced by a carbon‐arc method

The Kratschmer-Huffman carbon-arc method of preparing fullercnes has been used to generate carbon-coated transition metal (TM) and TM-carbide nanocrystallites. The magnetic nanocrystallites were extracted from the. soot with a magnetic gradient field technique. For TM=Co the majority of nanocrystals exist as nominally spherical particles, 0.5-S nm in radius. Hysteretic and temperature-dependent magnetic response, in randomly and magnetically aligned powder samples frozen in epoxy, correspond to fine particle magnetism associated with monodomain TM particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature T, . Below TR, the temperature dependence of the coercivity can be expressed as Hc=Hcu[ 1 - (T/TB)1’2], where HcO is the (1 K coercivity