The structure and magnetic properties of the nanoparticles of immiscible
system Co20Cu80 prepared by means of arc-discharge, have been
studied in detail. The diameters of the particles are about 20 ~ 30 nm
and a core/shell structure forms. The cores are Co-Cu solutions, which show
some small Co precipitates, encapsulated with a shell of cupper oxide or
cobalt oxide as observed by means of high-resolution transmission electron
microscope (HRTEM) and energy dispersive X-ray (EDS). The loop shift in the
hysteresis loop indicates the existence of the exchange bias between
ferromagnetic and antiferromagnetic components at low temperatures. A block
temperature about 180 K has been observed for as-deposited nanoparticles.
For the annealed nanoparticles, the thermal magnetization at low
temperatures is satisfied with Bloch's law.