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

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Abstract
The Krätschmer–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 TB. Below TB, the temperature dependence of the coercivity can be expressed as Hc=Hc0[1−(T/TB)1/2], where Hc0 is the 0 K coercivity.