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Designing heterogeneous interfaces and components at the nanoscale is proven effective for optimizing electromagnetic wave absorption and shielding properties, which can achieve desirable dielectric polarization and ferromagnetic resonances. However, it remains a challenge for the precise control of components and microstructures via an efficient synthesis approach. Here, the arc‐discharged plasma method is proposed to synthesize core@shell structural high‐entropy‐alloy@graphite nanocapsules (HEA@C‐NPs), in which the HEA nanoparticles are in situ encapsulated within a few layers of graphite through the decomposition of methane. In particular, the HEA cores can be designed via combinations of various transition elements, presenting the optimized interfacial impedance matching. As an example, the FeCoNiTiMn HEA@C‐NPs obtain the minimum reflection loss (RLmin) of −33.4 dB at 7.0 GHz (3.34 mm) and the efficient absorption bandwidth (≤−10 dB) of 5.45 GHz ranging from 12.55 to 18.00 GHz with an absorber thickness of 1.9 mm. The present approach can be extended to other carbon‐coated complex components systems for various applications.

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Carbon aerogels (CAs) are attractive candidates for the thermal protection of aerospace vehicles due to their excellent thermostability and thermal insulation. However, the brittleness and low mechanical strength severely limits their practical applications, and no significant breakthroughs in large CAs with a high strength have been made. We report a high-pressure-assisted polymerization method combined with ambient pressure drying to fabricate large, strong, crack-free carbon/carbon (C/C) composites with an excellent load-bearing capacity, thermal stability, and thermal insulation. The composites are comprised of an aerogel-like carbon matrix and a low carbon crystallinity fiber reinforcement, featuring overlapping nanoparticles, macro-mesopores, large particle contact necks, and strong fiber/matrix interfacial bonding. The resulting C/C composites with a medium density of 0.6 g cm–3 have a very high compressive strength (80 MPa), in-plane shear strength (20 MPa), and specific strength (133 MPa g–1 cm3). Moreover, the C/C composites of 7.5–12.0 mm in thickness exposed to an oxyacetylene flame at 1800 °C for 900 s display very low back-side temperatures of 778–685 °C and even better mechanical properties after the heating. This performance makes the composites ideal for the ultrahigh temperature thermal protection of aerospace vehicles where both excellent thermal-insulating and load-bearing capacities are required.

Compositing dielectric and magnetic components have been proven effective in optimizing electromagnetic (EM) wave absorption, in which the dielectric loss capacity can be reinforced by the polarization effects of hetero‐substitutions. Here, the dielectric polarization through the energy transformation between the relatively complex permeability and permittivity in nitrogen‐doped carbon nanocages (NCNs) with sub‐nanometer Fe clusters is further boosted. As a transition state between single Fe atoms and Fe3O4 nanoparticles hetero‐substitutions, these subnanometer Fe clusters confined in NCNs can be achieved by carbonizing FePc@ZIF‐8 composites at 900 °C. Benefitting from their unique structures, an enhanced dielectric loss tangent of 1.57 is obtained at 10 GHz, which is 3.0 and 1.6 times higher than those of single Fe atoms and Fe3O4 nanoparticles hetero‐substitutions, respectively. Furthermore, the minimum reflection loss can reach −64.75 dB at 7.1 GHz (2.7 mm) and the effective absorption bandwidth is 6.2 GHz (11.8–18 GHz, covering the full P‐band) at 1.7 mm. The present study provides intrinsic insight into the dielectric polarization behaviors in subnanometer hetero‐substitutions, inspiring the design of high‐performance EM absorption materials.

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Magnetic hopfions are three-dimensional topological solitons with a nontrivial Hopf index. Here, we theoretically investigated the spin excitation spectrum and revealed corresponding spin-wave modes of a magnetic hopfion. Compared with skyrmion tubes, the hopfions have distinctly less resonance peaks due to the suppression of vertical spin-wave modes by the internal topological defect. We also found that breathing and rotating modes could hybridize in hopfions under z-direction excitations and, thus, characterized the five individual resonance modes by a set of number pair (b, r). The results provide a fundamental understanding of the spin-wave modes of magnetic hopfions and open a route to detect and manipulate 3D topological solitons using microwave magnetic fields.