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.

Recent observations of topological meron textures in two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted considerable research interest for both fundamental physics and spintronic applications. However, manipulating the meron textures and realizing the topological transformations, which allow for exploring emergent electromagnetic behaviors, remain largely unexplored in 2D magnets. In this work, utilizing real-space imaging and micromagnetic simulations, we reveal temperature- and thickness-dependent topological magnetic transformations among domain walls, meron textures, and stripe domain in Fe5GeTe2 (FGT) lamellae. The key mechanism of the magnetic transformations can be attributed to the temperature-induced change of exchange stiffness constant within layers and uniaxial magnetic anisotropy, while the magnetic dipole interaction as governed by sample thickness is crucial to affect the critical transformation temperature and stripe period. Our findings provide reliable insights into the origin and manipulation of topological spin textures in 2D vdW ferromagnets.

Recently, tremendous efforts have been devoted to fabricating hollow micro-/nanostructures with tunable sizes, shapes, and Although assembled hollow architectures have received considerable attention as lightweight functional materials, their uncontrollable self-aggregation and tedious synthetic methods hinder precise construction and modulation. Therefore, this study proposes a bi-ion synergistic regulation strategy to design assembled hollow-shaped cobalt spinel oxide microspheres. Dominated by the coordinationetching effects of F − and the hydrolysis-complex contributions of NH 4 + , the unique construction is formed attributed to the dynamic cycles between metal complexes and precipitates. Meanwhile, their basic structures are perfectly retained after reduction treatment, enabling FeCo/CoFe 2 O 4 bimagnetic system to be obtained. Subsequently, in-depth analyses are conducted. Investigations reveal that multiscale magnetic coupling networks and enriched air-material heterointerfaces contribute to the remarkable magnetic-dielectric behavior, supported by the advanced off-axis electron holography technique. Consequently, the obtained FeCo/CoFe 2 O 4 composites exhibit excellent microwave absorption performances with minimal reflection losses (RL min ) as high as −51.6 dB, an effective absorption bandwidth (EAB) of 4.7 GHz, and a matched thickness of 1.4 mm. Thus, this work provides an informative guide for rationally assembling building blocks into hollow architectures as advanced microwave absorbers through bi-ion and even multi-ion synergistic engineering mechanisms.

Recently, two-dimensional magnetic material has attracted attention worldwide due to its potential application in magnetic memory devices. The previous concept of domain walls driven by current pulses is a disordered motion. Further investigation of the mechanism is urgently lacking. Here, Fe3GeTe2, a typical high-Curie temperature (T C) two-dimensional magnetic material, is chosen to explore the magnetic domain dynamics by in situ Lorentz transmission electron microscopy experiments. It has been found that the stripe domain could be driven, compressed, and expanded by the pulses with a critical current density. Revealed by micromagnetic simulations, all the domain walls cannot move synchronously due to the competition between demagnetization energy and spin-transfer torque effect. In consideration of the reflection of high-frequency pulses, the disordered motion could be well explained together. The multiple stable states of the magnetic structure due to the weak exchange interaction in a two-dimensional magnet provides complex dynamic processes. Based on plenty of experiments, a cluster of domain walls could be more steady and move more synchronously under the drive of pulse current. The complication of domain wall motions presents a challenge in race track memory devices and two-dimensional magnetic material will be a better choice for application research.