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

Abstract

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: f m ) of 0.54 and 0.64 GHz with the thickness (matching thickness: d m ) 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.

Microwave characteristics of Co/TiO2 nanocomposites prepared by mechanochemical synthesis

“…To overcome this shortcoming, an effective approach is to disperse magnetic metallic particles with size less than the skin depth in insulator matrix. Various material systems (e.g., ␣-Fe/Fe 3 B/Y 2 O 3 [3], Fe/SiO 2 [4], Co/SiO 2 [5], Co/PVP [6], Co x Ni (100−x) /MnO 2 [7,8], Ni/C [9]) have been attempted. The electrical resistivity of these systems can be enhanced by several orders and reach 10 4 cm [3]; and the eddy current effect can be suppressed effectively due to the presence of the insulator matrix.…”

Controlled Synthesis and Microwave Absorption Property of Chain-Like Co Flower

“…It is reported that Co nanochains can reach reflection loss peak about −11 dB at 17.2 GHz at the thickness of 2.5 mm, and Co nanoparticles can only reach the maximum reflection loss −5 dB in 2–5 GHz at the thickness of 3.16 mm [4], [5]. While chain-like Co flower at a thinner thickness of 2 mm as shown in Fig.…”

“…However, as a kind of representative magnetic material, only a few literatures have discussed the microwave absorption property of Co due to its poor microwave absorption ability. Kato et al has validated cobalt particles could only exhibit strong microwave absorption during very narrow frequency band [4], while Cao et al found hollow chain-like cobalt displayed absorption ability no stronger than −11 dB [5]. Therefore, it is valuable to deeply explore the microwave absorption mechanism of Co and find the route to improve its absorption.…”

Cobalt Nanoparticle Inks for Printed High Frequency Applications on Polycarbonate

“…The permeability of Co 2 (CO) 8 /polyvinyl-2-pyrrolidone (PVP) composite of 5 vol.% was 4.3, 10 vol.% 5.8, and 50 vol.% only 1.7 at 1 GHz. 26 The cobalt inks exhibited (in Fig. 5) a relative real permeability of 1.3-1.5 (45 MHz).…”