Varying the size and magnetic properties of carbon-encapsulated cobalt particles

Carbon-encapsulated cobalt particles were produced by a modified are-discha rge technique and subsequently purified with an acid treatment. The arc dis charge was realized between a graphite cathode and a graphite crucible with a solid Co target, under partial He pressure with an additional quenching jet. The produced particles are spherical and covered by typically 3-5 grap hitic carbon shells. The mean diameter could be varied between 5 and 45 nm by changing the deposition parameters (gas pressure and flow rate of the qu enching jet). The magnetic properties were analyzed with a variable tempera ture SQUID magnetometer. The encapsulated particles showed ferromagnetic hy steresis loops with marked size-dependent properties. (C) 2001 Elsevier Sci ence B.V. All rights reserved.