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

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 image value below 1.0, the image 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.