Coupling of 0D/1D Grain Boundaries Inducing Extreme Charge Rearrangement/Magnetic Resonance for Ultrabroadband Electromagnetic Wave Absorption

ABSTRACT Ferrite–carbon composites effectively absorb electromagnetic (EM) waves via coupled mechanisms. However, the dynamic evolution of intrinsic polarization and magnetic loss mechanisms following interfacial coupling has long been overlooked, impeding broadening of the ultra‐broadband EM wave absorption performance in heterostructures. Herein, via surface ligand modulation, in situ growth of 0D Fe ₃ O ₄ quantum dots (QDs) on the surface of 1D carbon nanotubes triggers grain boundary coupling. The energy rebalancing effect at the interface induces an extreme charge rearrangement within the Fe ₃ O ₄ QDs. This rearrangement enhances dipole orientation hysteresis and charge accumulation, resulting in charge and interfacial polarization losses. Meanwhile, for subcritical Fe ₃ O ₄ QDs, short‐range magnetic resonance and magnetic exchange–triggered magnetic resonance transfer synergistically enhance the magnetic loss. Through charge rearrangement/magnetic resonance induced by 0D/1D grain boundary coupling, an effective bandwidth of nearly 10 GHz is achieved at a minimal thickness of 2 mm, covering the X and Ku bands. This strategy provides an effective paradigm and novel theoretical insights for ultra‐broadband electromagnetic wave absorption applications.