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 11.5 muB, a blocking temperature of 2 K, and sigma(s) = 146 emu/g at 1.7 K. The magnetic moment and sigma(s) combined imply a particle size of about 5.4 angstrom. However, the particles made in the DDAB system were relatively large, approximately 10 nm. They were ferromagnetic at room temperature but with no coercivity.