Em. Brunsman et al., MAGNETIC-PROPERTIES OF CARBON-COATED, FERROMAGNETIC NANOPARTICLES PRODUCED BY A CARBON-ARC METHOD, Journal of applied physics, 75(10), 1994, pp. 5882-5884
The Kratschmer-Huffman carbon-arc method of preparing fullerenes has b
een used to generate carbon-coated transition metal (TM) and TM-carbid
e nanocrystallites. The magnetic nanocrystallites were extracted from
the soot with a magnetic gradient field technique. For TM = Co the maj
ority 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, cor
respond to fine particle magnetism associated with monodomain TM parti
cles. The magnetization exhibits a unique functional dependence on H/T
, and hysteresis below a blocking temperature T(B). Below T(B), the te
mperature 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.