Preparation and microwave absorption properties of spherical cobalt particles

Spherical cobalt particles with special morphology were prepared on a large scale through a simple and low-cost liquid reduction method. The morphology, crystal structure, static magnetic properties and electromagnetic behavior of the cobalt particles were measured by SEM, XRD, VSM and vector network analyzer, respectively. The results show that saturation magnetization of the Co particles is 123 (A·m²)/kg, less than that of hcp-Co single crystals, and the coercivity is 176 ×79.6 A·m^-1, larger than that of bulk cobalt crystals. Furthermore, dual-nonlinear dielectric resonances appear at 9.8 and 15 GHz. The real part of permeability decreases with the frequency increasing, presenting an excellent frequency dispersion property. Meanwhile, the imaginary part of permeability reveals a wide resonance peak over the microwave frequency range. According to the transmit-line theory, the reflection loss (RL) was predicted through the permittivity and permeability for a given frequency and absorber thickness. A maximum reflection loss of -13.2 dB is achieved at 12.4 GHz with a thickness of 5.5 mm, and the effective absorption bandwidth -10 dB) is 1.6 GHz, indicating the as-prepared cobalt particles have potential applications as a candidate for microwave absorption.