Ultrafine Cobalt-Iron Cyanide Particles Prepared by Microemulsion Method

Cobalt–iron cyanide particles having ferromagnetic behavior with a Curie temperature TC of 14 to 15 K can be precipitated by mixing CoIICl2 and K3FeIII(CN)6. This similar reaction was carried out in the water pools of reverse micelles. By using nonionic surfactant poly(oxyethylene)5 nonyl phenol ether (NP5) and poly(oxyethylene)9 nonyl phenol ether (NP9) and petroleum ether (PE), reverse micelles can be made with a water pool of specific size which can be usually varied by the water/surfactant ratio. Such combination of surfactant, oil and aqueous solution provides a unique reactor environment for the synthesis of molecular-based magnetic particles of narrow size distribution. Molecular-magnetic powders, K0.28Co1.29[Fe(CN)6] · 6.5 H2O with particle size ranging from 5 to 10 nm have been successfully synthesized by the water-in-oil microemulsion technique. These particles have a Curie temperature of ≈︂14 K as determined using the Curie-Weiss law. High coercivity of 1.8 kOe was also measured for the ultrafine powder at 4.2 K. Structural and magnetic properties of the resulting magnetic materials are reported. This work has shown that microemulsion can be a powerful process to synthesize ultrafine molecular magnet particles exhibiting high coercivity.