Magnetic Properties and Microwave Absorption Properties of Polymer-Protected Cobalt Nanoparticles ∗1

This paper describes magnetic properties and microwave absorption properties of polymer-protected cobalt nanoparticles. Cobalt nanoparticles were prepared using the thermal decomposition of dicobalt octacarbonyl in ethylene glycol. They were stabilized and dispersed by coexisting with poly(N -vinyl-2-pyrrolidone) (PVP), resulting in an average diameter of 45 nm. The X-ray diffraction (XRD) analysis revealed that the Co-PVP sample synthesized at 170◦C for 3 h, with the mole ratio of cobalt : PVP = 1 : 10 (mol : unit mole), consisted of two phases of hcp and fcc cobalt. Their saturation magnetization measured using a vibrating sample magnetometer (VSM) was 1.53×10−4 Wb·m·kg−1. The compacted sample, produced from the PVP-protected cobalt nanoparticles, showed a reflection loss (R.L.) less than −20 dB at the frequency (matching frequency: fm) of 0.54 and 0.64 GHz with the thickness (matching thickness: dm) of 6.16 and 5.04 mm, respectively. Therefore, it is concluded that polymer-protected cobalt nanoparticles have a possibility for the use as microwave absorption materials.