Surfactant-free synthesis and electromagnetic properties of Co-Ni-B composite particles

The Co-Ni-B composite particles with different mol ratio of Co to Ni were composited of spheres, spheres in-pair, hierarchical assemblies of dentrites, which were surfactant-free synthesized by chemical reduction method in aqueous solution. The complex permeability of the Co-Ni-B composite particles indicated reverse resonant peak at the frequency range of 8-16 GHz, where the complex permittivity showed the positive resonant peak and the μ_r″ of particles showed negative values, caused by the transformation between electric and magnetic energy. The imaginary parts of relative permeability (μ_r″) of Co-Ni-B composite particles indicated one broad resonant peak over the 2-8 GHz range for the high effective anisotropy. A slight decrease in complex permittivity resulted in an excellent impedance matching property. The Co-Ni-B composite alloy particles with mol ratio of 7:3 exhibited reflection loss less than -20 dB in frequency range of 4.0-14.5 GHz for the absorber thickness of 1.1-3.2 mm, and an optimal RL of -32.4 dB was obtained at 12.8 GHz with thickness of 1.2 mm. The broadest bandwidth of reflection loss less than -10 dB from 13.0 to 17.0 GHz, covering almost the whole Ku-band, was obtained for a thickness of 1.1 mm layer.