Sequential Architecture Induced Strange Dielectric‐Magnetic Behaviors in Ferromagnetic Microwave Absorber

Abstract

The high filler loading (FL) is a bottleneck in developing lightweight ferromagnetic microwave absorbers (MAs) for the actual applications. Sequential architecture design of MAs can induce strange physical behaviors due to the unique coupling‐enhancement effect between functional units, providing a vast potential for achieving high microwave absorption performance. However, the FLs of current sequential MAs fail to be designed on demand because the strange dielectric‐magnetic behaviors cannot be fulfilled. The influence of sequential architecture engineering on the macroscopic properties or microscopic loss mechanism still needs more exploration. Herein, based on four mesoscopic models (particles, chains, bundles, and fibers) of ferromagnetic functional units, a series of ferromagnetic MAs with different sequential architectures are prepared via a bottom‐up self‐assembly method. The fibrous samples exhibit the best microwave absorption performance (−51.3 dB, 4.12 GHz) at a breakthrough FL of 2 wt%, which is one order of magnitude less than other ferromagnetic MAs. Strange dielectric‐magnetic behaviors, including negative permittivity and heterodromous chiral vortex, occur due to functional units with lateral and fibrous configurations. Further, four special models are established to reveal the microwave attenuation evolutionary mechanism. This study clarifies the relationship between sequential architecture and strange dielectric‐magnetic behaviors, which provides new sight to understand microscopic electromagnetic loss mechanism.

Hierarchical Fe-Co@TiO2 with Incoherent Heterointerfaces and Gradient Magnetic Domains for Electromagnetic Wave Absorption

“…At nanoscale, the magnetization behavior, magnetic exchange force, and magnetic resonance of magnetic particles are closely related to the size distribution. For magnetic particle beyond the critical grain size, magnetic particles not only produce strong magnetic resonance and macroscopic magnetic coupling but also cause long-range magnetic diffraction resonance between adjacent regions. , If the size of magnetic particles is below the critical grain size, the short-range magnetic exchange force is greater than long-range magnetostatic force, which can interact with adjacent magnetic domains by the means of nanoscale magnetic bridge connection . As shown in Figure , the stray magnetic flux lines indicate that magnetic loss intrinsically correlates with Fe units beyond the critical grain size and Co particles with the scale domain below the critical grain size (Figure a). , Take Fe-Co microrods for example: it is proposed that these sub-microscale Fe domains act as magnetic activation antennas, and not only radiate out magnetic flux lines to interact with adjacent magnetic units by macroscopic magnetic coupling, but also radiate out magnetic flux lines into the opposite direction of the units themselves to realize long-range magnetic diffraction resonance, and both of them establish more connected magnetic networks to interfere with incident electromagnetic wave to dissipate electromagnetic energy, as presented in Figure b.…”

“…Significantly, hybrid composites with a hierarchical structure have been considered as the preferred candidates owing to the cooperative advantages of a multiloss mechanism and multiple scattering. − However, the generally accepted magnetic coupling in clarifying the magnetic loss mechanism is immensely blocked by the nonuniform size distribution with ambiguous resonance behavior. For micro-/submicroscale magnetic domains beyond the critical grain size, separated magnetic units not only radiate out magnetic flux lines to interact with neighbored analogues, usually defined as macroscopic magnetic coupling, , but also radiate out magnetic flux lines into the free space to realize long-range magnetic diffraction . On the contrary, for magnetic units below the critical grain size, short-range magnetic exchange interaction is larger than long-range magnetostatic ones .…”

Nanolayered Ceramic-Confined Graphene Aerogel with Conformal Heterointerfaces for Low-Frequency Microwave Absorption

“…Furthermore, the The EMW absorption performance is typically assessed by the RL and EAB (the bandwidth where RL < −10 dB). 42 The RL plots for the GA/C samples are presented in Figure 5a−f and can be calculated using eqs S5 and S6. Compared with pure rGO aerogel and SiCN ceramic (Figure S4), the RL min value of the GA/C-1 sample reaches −15.2 dB with a corresponding thickness of 5.0 mm at an ultralow frequency of 4 GHz, and the EAB covers a range of 1.20 GHz from 3.56 to 4.76 GHz.…”

“…The EMW absorption performance is typically assessed by the RL and EAB (the bandwidth where RL < −10 dB) . The RL plots for the GA/C samples are presented in Figure a–f and can be calculated using eqs S5 and S6.…”

Integrated Electromagnetic Device with On‐Off Heterointerface for Intelligent Switching Between Wave‐Absorption and Wave‐Transmission

“…[ 46 ] The surfaces of the conductive fillers are eventually charged due to the difference in Fermi levels or chemical potentials between the conductive fillers and the polymer binders. [ 47 ] Therefore, at room temperature, VO 2 (M) exists, and the insulating characteristics of VO 2 (M) fail to generate the Stern layer with PMDS at their heterointerface, resulting in interface polarization dominance of the heterointerface between V 2 C and VO 2 (M). When reaching the phase transition temperature, VO 2 (M) transforms into VO 2 (R) and the metallic properties of VO 2 (R) generate the Stern layer, resulting in reinforced polarization loss compared to the room temperature.…”