Parallel Aligned Nickel Nanocone Arrays for Multiband Microwave Absorption

Abstract

Magnetic nanostructures with conical shape are highly desired for pursuing extraordinary magnetic properties and microwave absorption. However, the fabrication of such nanostructures with controlled shape and size uniformities and alignment is not yet realized. Accordingly, the magnetic properties and their application as microwave absorber are not well understood. Here, we report on the first demonstration of controlled fabrication of soft magnetic nickel nanocone arrays with sharp geometry, large aspect ratio, uniform size, and parallel alignment. The imaginary part of the relative complex permeability shows multiband absorption in the 2−17 GHz range. Such an exceptional microwave absorption results from the uniform conical shape and size and the parallel alignment. The absorption mechanisms are discussed under the framework of natural resonance and exchange resonance. The natural resonance is dependent on the shape anisotropy and facilitated by the conical geometry. The exchange resonance is well explained by the observation of the bulk spin waves with exchange coupling at the tip of nanocones using the inelastic light scattering and is consistent with exchange theory predictions for the quantization of bulk spin waves. We expect that our work will shed light on the physical insights into the magnetic properties of nanocones and find great potential in applications of microwave absorption.

Enhanced Electromagnetic-Wave Absorbing Performances and Corrosion Resistance via Tuning Ti Contents in FeCoNiCuTix High-Entropy Alloys

“…With the purpose of exploring the dissipating mechanisms during the interaction between the absorber and incident microwaves, Cole−Cole semicircle patterns (Figure 6b) and C 0 curves (C 0 = μ′(μ″) −2 f −1 , Figure 6c) are plotted. In the microwave frequency range, dipole relaxation polarization, which is caused by the rotation of the dipole moment in the direction of an electric field, can be expressed using the Debye equation: 40,41…”

“…With the purpose of exploring the dissipating mechanisms during the interaction between the absorber and incident microwaves, Cole–Cole semicircle patterns (Figure b) and C 0 curves ( C 0 = μ′(μ″) −2 f –1 , Figure c) are plotted. In the microwave frequency range, dipole relaxation polarization, which is caused by the rotation of the dipole moment in the direction of an electric field, can be expressed using the Debye equation: , where ε s is the static dielectric constant and ε ∞ is the dielectric constant of infinite frequency and τ is the relaxation time. The Cole–Cole semicircle can be obtained according to the deduced eq .…”

Two-Dimensional Basalt/Ni Microflakes with Uniform and Compact Nanolayers for Optimized Microwave Absorption Performance

“…Meanwhile, Ni is low-cost and relatively stable in air, satisfying practical application. The EM loss of Ni can be efficiently adjusted by tailoring the morphological structure, such as Ni chains, , Ni nanofibers, Ni hollow structures, Ni microflowers, Ni nanocone, Ni octahedra, sponge-like Ni flakes, etc., while magnetic Ni as absorbers surfers from high density, large filling load, and poor impedance matching. It will obtain a weak dielectric loss when the filling ratio of Ni is below the percolation threshold and high electrical conductivity when the filling ratio exceeds the percolation threshold .…”

Enhanced Microwave Absorption of Shape Anisotropic Fe3O4 Nanoflakes and Their Composites

“…[22,23] The construction of Fe 3 O 4 nanostructures was a conventional approach to solve this problem, in which a lower percolation threshold was attained to yield better electrical conductance loss, [24,25] while the shape anisotropy was obtained to enhance the magnetic loss. [21,[26][27][28] Some anisotropic Fe 3 O 4 structures, such as nanowires, [26,29,30] nanotubes, [21,31] and flakes, [23] were realized by electrospinning, solvothermal, and temple-assisted methods, which had demonstrated excellent microwave absorbing properties. Similar to the popular 2D high-performance MAMs with atom-level thickness (e.g., graphene and MXenes [2D transition-metal carbides and nitrides]), quasi-2D Fe 3 O 4 nanoflakes (FNFs) with nanoscale thicknesses could induce multiple scatterings between the hierarchical structures and produce longer electrical attenuation paths in the conductive networks, which could apparently enhance the EM loss.…”