Magnetic-dielectric synergistic coral-like CoNi@SiO2 microparticles for high-efficiency and broadband microwave absorption

Magnetic-dielectric functional materials with unique three-dimensional (3D) anisotropic structures, reasonable component regulation, and hierarchical heterogeneous interfaces are potential candidates for achieving efficient microwave absorption (MA). In this paper, CoNi/SiO₂ hybrids are synthesized for high-performance MA by anchoring the dielectric SiO₂ layer by Stöber's sol-gel method to regulate the permittivity (ε_r). The results show that the abundant pores and high specific surface area of the coral-like spherical structure, the ε_r modulation of CoNi alloy by SiO₂ shell-layer, the heterogeneous interface and charge storage capacity difference between both, which provide more reflective and scattering channels for the incident electromagnetic wave (EMW), optimize the impedance matching and enhance the interfacial polarization loss and magnetic loss, and finally achieve the reflection loss (RL) enhancement and effective absorption bandwidth (EAB) broadening. In particular, the coral-like CoNi@SiO₂-2 microparticle (MP) has the strongest RL of −66.59 dB at 2.2 mm matching thickness and the maximum EAB of 6.460 GHz at 1.9 mm matching thickness, which covers the entire Ku-band. In this study, the hierarchical heterostructure is constructed by a unique morphology design and the introduction of a dielectric anchoring layer, which provides a new way to prepare efficient microwave-absorbing materials by magnetic-dielectric coupling engineering.