Magnetic and microwave absorption properties of Ni microcrystals with hierarchical branch-like and flowers-like shapes

• Highly uniform flowers-like Ni spheres was synthesized by hydrothermal method.
• Flowers-like Ni sample exhibits an excellent microwave absorption in 2–18 GHz.
• Fowers-like Ni sample has a relatively low eddy current in 2–18 GHz.
• Fowers-like sample has a larger electric resistivity due to particle shape effect.

The Ni microcrystals with hierarchical branch-like and flowers-like shapes have been fabricated by hydrothermal method. The flowers-like microspheres with an average diameter of 500 nm are built of intercrossed flakes. Magnetic study of the Ni microcrystals indicates that the flowers-like microspheres sample has a little higher coercive force (276 Oe) than that of the branch-like sample (161 Oe). An important application of these hierarchical Ni microcrystals is used as high-performance microwave absorbers in 2–8 GHz range. Compared to the branch-like sample, flowers-like microspheres sample exhibits more excellent microwave absorbing performance and the reflection loss reaches a minimum of −17 dB at 13 GHz with −6 dB bandwidth covering the 6.5–14 GHz range. The further analysis of electromagnetic parameters indicates the branch-like sample has a significant eddy current effect which leads to the μ′μ′ value below 1.0, the μ″μ″ value below zero and the poor microwave absorption in 11.5–14 GHz range. However, flowers-like microspheres sample has relatively low eddy current effects coming from the particle shape effects, which results in relatively high permeability and more suitable impedance matching between permittivity and permeability in 2–18 GHz range.

The highly uniform flowers-like Ni spheres with an average diameter of 500 nm are successfully prepared by hydrothermal method. The flowers-like Ni sample exhibits a strong microwave absorption in 11.5–14 GHz range besides the absorption peak in 2–8 GHz range, moreover, the absorption frequency ranges of sample can be tuned easily by varying the coating layer thickness. Compared to the branch-like sample, flowers-like spheres sample exhibits relatively low permittivity, relatively high permeability and more excellent microwave absorption in the whole 2–18 GHz due to the relatively low eddy current coming from the particle shape effects because of flowers-like sample exhibits a higher electric resistivity.Figure optionsDownload as PowerPoint slide