Two-dimensional materials, especially the newly emerging MXene, have attracted numerous interests in the fields of energy conversion/storage and electromagnetic shielding/absorption. However, the inherently inevitable aggregation and absence of magnetic loss of MXene considerably limit its electromagnetic absorption application. The introduction of magnetic component and favorable structural engineering are the alternatives to improve the microwave absorption (MA) performance. Herein, we report a spheroidization strategy to assemble double-shell MXene@Ni microspheres, where the commonly lamellar MXene are reshaped into three-dimensional microspheres that provide the substrate for oriented growth of Ni nanospikes. Whereas this structural feature offers massive accessible active surfaces that effectively promote the dielectric loss ability, the introduction of magnetic Ni nanospikes enables the additional magnetic loss capacity. Benefiting from these merits, the synthesized 3D MXene@Ni microspheres exhibit superior MA performance with the minimum reflection loss value of −59.6 dB at an ultrathin thickness (∼1.5 mm) and effective absorption bandwidth of 4.48 GHz. Moreover, the electron holography results reveal that the high-density anisotropy magnetism plays an important role in the improvement of MA performance, which provides an insight for the design of MXene-based materials as high-efficient microwave absorbers.

Hierarchical engineering of suitable dielectric-magnetic multicomponents shows good performance for microwave absorbers, but still face bottlenecks. Herein, hierarchical double-shelled nanotubes (DSNTs), in which the inner magnetic tubular subunits are assembled by magnetic-heteroatomic components through cation-exchange reactions, and the outer dielectric MnO 2 nanosheets strengthen the synergistic interactions between confined heterogeneous interfaces are ingeniously designed and constructed. Heterointerfaces induced polarization is proposed to investigate the interfacial relaxation mechanism, and magnetic loss, closely related to the micrometerscale magnetic units, is mainly clarified by the magnetic interaction composed of magnetic coupling and magnetic diffraction; both of them are clearly confirmed by Lorentz off-axis electron holography. The obtained hierarchical DSNTs demonstrate efficient microwave absorption with an optimal reflection loss of −54.7 dB and qualified absorption bandwidth of 9.5 GHz owing to desirable heterogeneous interfaces, multiple magnetic heteroatomic components and hollow hierarchical microstructures. This strategy inspires a generalized methodology for the engineering of hollow hierarchical configurations with multishells, the combination of proposed hetero-interfaces induced polarization and microscale magnetic interaction broadens the dielectricmagnetic synergistic mechanism of the topography-performance relationship for microwave absorption materials.

The rational design of magnetic composites has great potential for electromagnetic (EM) absorption, particularly in the low-frequency range of 2-8 GHz. However, the scalable synthesis of such magnetic absorbers with both high magnetic content and good dispersity remains challenging. In this study, a confined diffusion strategy is proposed to fabricate functional magneticcarbon hollow microspheres. Driven by the ferromagnetic enhanced Kirkendall diffusion effect, the in situ alloying of FeCo nanoparticles is tightly confined in carbon shells, effectively inhibiting magnetic agglomeration. Moreover, the core-shell FeCo-carbon nano-units further assemble into dispersive microscale magnetic-carbon Janus bulges on both the inner and outer surfaces of the hollow microsphere. The optimized hollow FeCo@C microspheres exhibit excellent low-frequency EM wave absorption performance: the minimum reflection loss (RL min ) is −35.9 dB, and the absorption bandwidth covers almost the entire C-band. Systematic investigation reveals that the large size of the magnetic-carbon integration, high-density confined magnetic units, and strong magnetic coupling are essential for enhancing the magnetic loss dissipation of low-frequency EM waves. This study provides a novel strategy for fabricating advanced EM wave absorbers and significant inspiration for investigating the magnetic attenuation mechanism at low frequency.

Severe lower‐frequency (2–8 GHz) microwave pollution caused by the rapid development of 5th generation (5G) communication posts significance on cutting‐edge microwave absorbers. However, the intensely coupled wave‐impedance and microwave dissipating ability dramatically hinder their performance in the exact lower‐frequency range. The rationally designed heterostructure of hard/soft ferrite composite provides an efficient solution to address the issue. In this context, core‐shell structured hard/soft BaFe(12‐x)CoxO19@Fe3O4 with abundant heterointerface is created using facile spray‐drying and subsequent solvothermal approach, where hard magnetic BaFe(12‐x)CoxO19 serves as the core and soft magnetic Fe3O4 serves as the shell, respectively. The unique core‐shell integration contributes sufficient magnetic exchange coupling interaction for strong magnetic loss beyond Snoek's limitation, which considerably boosts a lower‐frequency microwave absorption. Accordingly, the minimum reflection loss (RLmin) of typical BaFe11.6Co0.4O19@Fe3O4 microcomposite reaches −48.9 dB at the thickness of 3.5 mm, its bandwidth of reflection loss < −10 dB can cover almost all the S and C bands (2.6–8 GHz). Generally, an easy and controllable pathway is conveyed in this work to encourage improved magnetic loss ability as well as decouple the wave‐impedance and microwave dissipating ability in magnetic composites, which widens the road to the development of advanced lower‐frequency magnetic absorbers.

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Rational designing of one-dimensional (1D) magnetic alloy to facilitate electromagnetic (EM) wave attenuation capability in low-frequency (2–6 GHz) microwave absorption field is highly desired but remains a significant challenge. In this study, a composite EM wave absorber made of a FeCoNi medium-entropy alloy embedded in a 1D carbon matrix framework is rationally designed through an improved electrospinning method. The 1D-shaped FeCoNi alloy embedded composite demonstrates the high-density and continuous magnetic network using off-axis electronic holography technique, indicating the excellent magnetic loss ability under an external EM field. Then, the in-depth analysis shows that many factors, including 1D anisotropy and intrinsic physical features of the magnetic medium-entropy alloy, primarily contribute to the enhanced EM wave absorption performance. Therefore, the fabricated EM wave absorber shows an increasing effective absorption band of 1.3 GHz in the low-frequency electromagnetic field at an ultrathin thickness of 2 mm. Thus, this study opens up a new method for the design and preparation of high-performance 1D magnetic EM absorbers.

Dielectric polarization and magnetic resonance associated with intrinsic constituent and extrinsic structure are two kinds of fundamental attenuation mechanisms for microwave absorbers, but remain extremely challenging in revealing the composition-morphology-performance correlation. Herein, hierarchical MXene/metal-organic framework derivatives with coherent boundaries and magnetic units below critical grain size are constructed to realize synergistic dielectric-magnetic enhancement by phase-evolution engineering and dynamic magnetic resonance. Specifically, phase-evolution induced inseparable interfaces, diverse incompatible phases, and defects/ vacancies contribute to dielectric polarization, while closely distributed magnetic units simultaneously realize nanoscale multi-domain coupling and long-range magnetic interaction. As results, the hierarchical derivatives promise an exceptional reflection loss of −59.5 dB and an effective absorption bandwidth of 6.1 GHz. Both experimental results and theoretical calculations indicate that phase-evolution engineering and dynamic magnetic resonance maximize the absorption capability and demonstrate a versatile methodology for manipulating microwave attenuation. More importantly, the proposed multi-domain coupling and long-range magnetic interaction theories innovatively offer dynamic magnetic resonance mechanism for magnetic loss within critical grain size.

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