Abstract
A process based on the Kratschmer-Huffman carbon arc method of preparing fullerenes has been used to generate carbon-coated cobalt and cobalt carbide nanocrystallites. Magnetic nanocrystallites are extracted from the soot with a gradient field technique. For Co/C composites, structural characterization by x-ray diffraction and high-resolution transmission electron microscopy reveals the presence of a fcc Co phase, graphite, and a minority C phase. The majority of Co nanocrystals exists 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 reveals fine-particle magnetism associated with monodomain Co particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature, ≃160 K. Below , the temperature dependence of the coercivity is given by =[1-(T/], with ≃450 Oe.
- Received 12 October 1993
DOI:https://doi.org/10.1103/PhysRevB.49.11358
©1994 American Physical Society