Processing and properties of magnetic nanoparticles encapsulated in carbon shells

The chemical composition, structure and magnetic properties of nanoparticles obtained by arc discharge between carbon electrodes containing Nd-Fe-Nb-B catalyst were investigated. The samples, which were obtained, consisted of magnetic nanocrystallites covered by carbon shells. The products were collected from the cathode (deposit) and reactor walls (soot). The arc discharge process was carried out with various erosion rates. The magnetic properties depend on both the point of collection and the erosion rate. The mean coercivity in the deposit is about 50 kA/m. The coercivity in the soot strongly depends on the erosion rate and, for a rate of 1.45 g/min, achieves a maximum value of 88 kA/m. The variation of the coercivity with erosion rate points to the formation of various phases in the particles, depending on the processing variables and point of deposition. (c) 2005 Elsevier B.V. All rights reserved.