Dependency of magnetic microwave absorption on surface architecture of Co₂₀Ni₈₀hierarchical structures studied by electron holography

Abstract

To design and fabricate rational surface architecture of individual particles is one of the key factors that affect their magnetic properties and microwave absorption capability, which is still a great challenge. Herein, a series of Co20Ni80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chain-like morphologies, were obtained using structure-directing templates via a facile one-step solvothermal treatment. The microwave reflection loss (RL) of urchin-like Co20Ni80 hierarchical structures reaches as high as -33.5 dB at 3 GHz, with almost twice the RL intensity of the ball- and chain-like structures, and the absorption bandwidth (<-10 dB) is about 5.5 GHz for the flower-like morphology, indicating that the surface nanospikes and nanoflakes on the Co20Ni80 microsphere surfaces have great influences on their magnetic microwave absorption properties. Electron holography analysis reveals that the surface nanospikes and nanoflakes could generate a high density of stray magnetic flux lines and contribute a large saturation magnetization (105.62 emu g(-1) for urchin-like and 96.41 emu g(-1) for flower-like morphology), leading the urchin-like and flower-like Co20Ni80 to possess stronger microwave RL compared with the ball-like and chain-like Co20Ni80 alloys. The eddy-current absorption mechanism μ''(μ')(-2)(f)(-1) is dominant in the frequency region above 8 GHz, implying that eddy-current loss is a vital factor for microwave RL in the high frequency range. It can be supposed from our findings that different surface morphologies of magnetic hierarchical structures might become an effective path to achieve high-performance microwave absorption for electromagnetic shielding and stealth camouflage applications.

Effect of aspect ratio on dielectric, magnetic, percolative and microwave absorption properties of magnetite nanoparticles

“…Guo and co-workers fabricated self-assembled flowerlike aFe 2 O 3 and c-Fe 2 O 3 with similar size and morphology to study the effect of crystalline structure on EM properties [18]. Liu et al synthesized a series of Co 20 Ni 80 hierarchical structures with different surface morphologies, including flower-, urchin-, ball-, and chainlike morphologies to study the dependency of microwave absorption on architectural characteristics of particles [25].…”

Facile synthesis of (Ni,Co)@(Ni,Co)xFe3−xO4 core@shell chain structures and (Ni,Co)@(Ni,Co)xFe3−xO4/graphene composites with enhanced microwave absorption

“…induce magnetic interactions between the neighboring particles, which will improve the absorption performance. 33,34 The interfacial polarization is induced by multiple interfaces in the (Ni,Co)@(Ni,Co) x Fe 3-x O 4 core@shell structures, and the chargecarrier transfers between Ni, Co and (Ni,Co) x Fe 3-x O 4 may also play a critical role to the improvement of the microwave absorption properties. 21,35,36 Figure 5b shows the calculated reflection loss of (Ni,Co)@Ni,Co) x Fe 3-x O 4 /graphene based sample (sample II).…”

Dependency of tunable microwave absorption performance on morphology-controlled hierarchical shells for core-shell Fe3O4@MnO2 composite microspheres

“…Hierarchical three-dimensional flower-like Co/CoO composites have enabled an optimal reflection loss value of -50.0 dB (7.2 GHz) and a broad effective bandwidth ranging from 13.8 to 18 GHz [14]. Moreover, among the three hierarchical Co 20 Ni 80 microspheres with different morphologies, the urchin-like ones displayed the minimum reflection loss value of -33.5 dB (3.0 GHz) while the flower-like ones possessed the absorption bandwidth of 5.5 GHz [15]. Thus it can be seen that hierarchical architecture is in favor of electromagnetic energy attenuation in the absorbing materials.…”