Magnetic properties of cobalt and cobalt-platinum alloy nanoparticles synthesized via microemulsion technique

Metallic cobalt and cobalt-platinum alloys of various nanometer sizes have been synthesized via the microemulsion technique and their magnetic propert ies have been characterized. Preparation of cobalt and cobalt-platinum allo y nanoparticles was achieved by reducing aqueous metallic salts confined in the polar regions of the reverse micelle of cetyltrimethyl bromide (CTAB) with sodium borohydride. These particles are further coated with gold by re ducing aqueous gold salts with borohydride. The dc susceptibility data of 1 5 mn gold coated Co, CoPt and COPt3 particles exhibit a blocking temperatur e of 4 K, 80 K and 106 K and coercivity of 20 Oe, 200 Oe, and 415 Oe at 10 K, respectively. Annealing these samples at 400 degreesC further enhanced t heir magnetic properties. The two cobalt-platinum alloys have been synthesi zed and characterized by x-ray powder diffraction and transmission electron microscopy.