Shell/core structure and magnetic properties of carbon-coated Fe-Co(C) nanocapsules

Abstract

Shell-core structures of Fe(C), Co(C) and Fe-Co(C) nanocapsules, prepared by an arc discharge process in a mixture of methane and helium, have been demonstrated by means of high-resolution transmission electron microscopy (HRTEM). These nanoscale magnetic cores are protected by graphite shells. It has been found that the zero-field-cooled (ZFC) magnetization of Fe-Co(C) nanocapsules that display different characteristics in three temperature ranges can be well interpreted in terms of the unblocking of magnetization of small single-domain particles and the depinning of large multidomain particles. The saturation magnetization of these nanocapsules decreases monotonically, while the coercivity decreases significantly with increasing temperature.