Magnetic properties of microemulsion synthesized cobalt fine particles

Two microemulsion systems, the ternary system H2O/AOT/isooctane and the binary system DDAB/toluene, were used to prepare metallic cobalt particles by borohydride reduction of a cobalt salt. The particles prepared in the AOT system were extremely small and superparamagnetic with magnetic moment per particle of 11.5μB, a blocking temperature of 2 K, and σs=146 emu/g at 1.7 K. The magnetic moment and σs combined imply a particle size of about 5.4 Å. However, the particles made in the DDAB system were relatively large, ∼10 nm. They were ferromagnetic at room temperature but with no coercivity.