Excellent NiO–Ni Nanoplate Microwave Absorber via Pinning Effect of Antiferromagnetic–Ferromagnetic Interface

Materials with strong magnetic property that can provide excellent microwave absorption performance are highly desirable, especially if their dielectric and magnetic properties can be easily modulated, which make minimal thickness and ultrawide bandwidth become achievable. The magnetic properties of ferromagnetic (FM) and antiferromagnetic (AFM) composite materials are closely related to their ratio of composition, size, morphology, and structure. AFM–FM composites have become a popular alternative for microwave absorption; however, the controllable design and preparation need to be urgently optimized. Here, we have successfully prepared a series of platelike NiO–Ni composites and demonstrated the potential of such composites for microwave absorption. Strong magnetic coupling was found from NiO–Ni nanoparticles by electron holography, which makes NiO–Ni composites a highly efficient microwave absorber (strong reflection loss: −61.5 dB and broad bandwidth: 11.2 GHz, reflection loss < −10 dB). Our findings are helpful to develop a strong microwave absorber based on magnetic coupling

“Matryoshka Doll”-Like CeO₂ Microspheres with Hierarchical Structure To Achieve Significantly Enhanced Microwave Absorption Performance

Recently, it is still a great challenge to develop a new type of absorber that possesses special advantages of low cost, ultrawide bandwidth, and strong absorption intensity. Herein, the unique “Matryoshka doll”-like CeO₂ microspheres with tunable interspaces were successfully synthesized by a facile and template-free method. The as-synthesized hierarchical yolk–shell CeO₂ microspheres were constructed by a layer of outer shell and multiple inner cores. The interspace gap of the microspheres can be simply adjusted only by altering the solvothermal reaction time. Simultaneously, Ostwald ripening, Kirkendall effect, and self-etching process contribute a synergetic growth mechanism responsible for this amazing hierarchical architecture. Importantly, the “Matryoshka doll”-like CeO₂ microspheres exhibited significantly strong microwave absorption in the frequency range of 2–18 GHz, with a reflection loss of −71.3 dB at 14.5 GHz and an effective absorption bandwidth of 5.4 GHz (<−10 dB), which is superior to the multicomponent absorbers. Such an outstanding microwave absorption performance stems from the unique hierarchical yolk–shell structure and the designable interspaces, leading to the multiple scattering, interfacial polarization, and plasma dielectric oscillation from the abundant interfaces and curved surfaces, which can be illustrated by the related results from electron holography and electron energy loss spectroscopy. To the best of our knowledge, the “Matryoshka doll”-like CeO₂ microspheres with a facile synthesis process, low cost, and excellent microwave absorption performance are believed to be an optimal candidate of single-component absorbers and helpful in the study of absorption mechanism