MAGNETIC-PROPERTIES OF CARBON-COATED, FERROMAGNETIC NANOPARTICLES PRODUCED BY A CARBON-ARC METHOD

The Kratschmer-Huffman carbon-arc method of preparing fullerenes 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, 0.5-5 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(B). Below T(B), the temperature dependence of the coercivity can be expressed as H(c) = H(c0)[1 - (T/T(B))1/2], where H(c0) is the 0 K coercivity.