Abstract
Microwave radar absorbing materials have been the focus of the radar stealth research field. In this study, ceramic structured porous honeycomb-like Al2O3 film was prepared by anodic oxidation, and an Ni layer was deposited on the Al2O3 film via electrodeposition in a neutral environment to form a flower- and grain-like structure in a three-dimensional (3D) network Ni/Al2O3/Ni film. The films both have a through-hole internal structure, soft magnetic properties, and absorb microwaves. The dielectric loss values of two films were little changed, and the maximum microwave absorption values of flower- and grain-like Ni/Al2O3/Ni film were −45.3 and −31.05 dB with relatively wide effective bandwidths, respectively. The porous ceramic structure Al2O3 interlayer prevented the reunion of Ni and isolated the eddy current to improve the microwave absorption properties. The material presented in our paper has good microwave absorption performance with a thin thickness, which indicates the potential for lightweight and efficient microwave absorption applications.
Highlights
Magnetic overlapping multilayer films formed by alternately depositing ferromagnetic materials on an insulating material substrate have good chemical stability, a tunnel magnetoresistance effect, and a microwave absorption function [1]
According to the giant magnetoresistance (GMR) in thin film structures composed of alternating ferromagnetic and nonmagnetic layers [4], as adjacent magnetic layers are always separated by non-magnetic layers, the coupling pattern of magnetic moments of adjacent layers usually changes from anti-parallel or disordered arrangement to parallel arrangement under the action of an external magnetic field, which may be caused by a non-magnetic isolation structure or the change in an internal magnetic field
The microwave absorption of the flower-like Ni/Al2 O3 /Ni film sample was mainly due to the presence of porous Ni, and we think that Al2 O3 acted as an insulating phase to block the interaction of Ni particles and avoid the eddy current effect (Figure 9)
Summary
Magnetic overlapping multilayer films formed by alternately depositing ferromagnetic materials on an insulating material substrate have good chemical stability, a tunnel magnetoresistance effect, and a microwave absorption function [1]. The exploration of this artificial nanostructure has broadened the research field of magnetic transmission theory [2,3]. Kang et al [6] proved that the soft magnetic properties of porous carbon nanotubes significantly improved after filling with ferromagnetic metals. Other research showed that using Al2 O3 as an insulating layer for magnetic particles can improve the microwave stealth ability of magnetic materials [7]. Wei et al prepared an Fe3 Al composite using a mechanochemical method and coated Al2 O3 as an insulating layer on the surface of Fe3 Al
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