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

Carbon-encapsulated cobalt particles were produced by a modified arc-discharge technique and subsequently purified with an acid treatment. The arc discharge 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 graphitic 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 quenching jet). The magnetic properties were analyzed with a variable temperature SQUID magnetometer. The encapsulated particles showed ferromagnetic hysteresis loops with marked size-dependent properties.