Synthesis, magnetic resonance and microwave absorption properties of cobalt nanospheres

By using a simple and low-cost liquid reduction method, we have synthesized cobalt nanospheres on a large scale. The materials were characterized, and the result showed that as-prepared products were cobalt nanospheres, assembled by nanosheets in parallel, with a size of around 100 nm. The electromagnetic behaviors of the cobalt nanospheres, including permittivity (ε_r = ε′ - jε″) and permeability (μ_r = μ′ - jμ″), were also investigated as a function of frequency in the microwave frequency range of 2-18 GHz. The permittivity presented multiple dielectric resonance peaks whilst the permeability displayed dual obvious magnetic resonance peaks, manifestly different from other cobalt particles in comparison. The calculated reflection loss (RL) indicated there were two strong microwave absorption peaks over the microwave frequency range of 2-18 GHz, which was in accord with the magnetic resonance peaks. The result revealed that the magnetic loss contributed even more than dielectric loss to the microwave absorption for the cobalt nanospheres.