Nanocrystalline Co30Fe70 alloy synthesized by alkalide reduction

Co30Fe70 nanocrystallites have been synthesized by alkalide co-reduction of Co2+ and Fe3+. As produced, the material consists of highly pyrophoric 4.0 nm nanocrystals with a narrow (< 12%) size distribution, that are superparamagnetic with an average blocking temperature <T-B> of similar to 20 K prior to removal of the by-products in which they are embedded. Removal of the by-products allows magnetic interactions between the particles with a consequent increase in the transition temperature to greater than 300 K. Annealing at temperatures higher than 300 degrees C under vacuum resulted in agglomeration and particle growth; annealing above 500 degrees C resulted in a change in the shape of the particles to largely rectangular prisms with little further growth above 700 degrees C. M-s increased with increasing annealing temperature reaching values as large as similar to 89% of the bulk value ( 245 emu/g) after annealing at 700 degrees C while retaining low M-r and H-c. While rapid exposure of the Co30Fe70 nanocrystallites to air resulted in spontaneous combustion, gradual, slow exposure over a period of one week resulted in the formation of a thin surface coating of CoFe2O4, or air stable "core-shell'' alloy-oxide nanocrystallites.