ENCAPSULATED NANOPARTICLES OF IRON METAL

Metastable iron-magnesium particles as intimate mixtures were prepd. b y co-depositing Fe and Mg vapors with a hydrocarbon diluent at 77 K, f ollowed by warming to room temperature. Upon heat treatment phase segr egation was accomplished with reasonable control. Core-shell particles (Fe as core) were formed, where Fe particles were encapsulated, and w ith appropriate heat treatment could be completely protected from surf ace oxidation. Crystallite sizes of the Fe core ranged from 3 to 26 nm depending on the heat treatment procedure. The magnetic properties of these encapsulated particles indicated extremely soft ferromagnetism with very low coercivities and with little size dependency. These resu lts coupled with earlier findings suggest that coercivity can be contr olled (dominated) by surface coating in such small particles.