Interfacial Electron Transfer Boosts Magnetic/Dielectric Synergy in Boron Nitride@Carbon/Fe Heterostructures for Efficient Low‐Frequency Electromagnetic Dissipation and Thermal Transport

The rapid development of fifth‐generation (5G) communication technology has intensified issues related to electromagnetic radiation and heat accumulation, driving a demand for polymer‐based composites incorporating dual‐functional fillers for concomitant low‐frequency electromagnetic wave absorption (EWA) and thermal conduction. However, achieving such dual functionality remains difficult due to the inherent trade‐offs among impedance matching, low‐frequency attenuation capability, and efficient heat transfer. To address this challenge, a facile carbon‐heterointerface engineering strategy is proposed to bridge the insulating thermally conductive boron nitride (BN) and magnetic Fe nanoparticles. It demonstrates that the carbon interlayer promotes electron transfer from Fe nanoparticles to the adjacent BN/C heterointerface, and also reduces thermal resistance between the BN and Fe nanoparticles. Benefiting from the improved impedance matching, interfacial electron transfer, and magnetic‐dielectric synergy within the well‐defined heterointerfaces, the BN@NC/Fe‐3 composite blended with epoxy resin exhibits excellent low‐frequency EWA performance with a minimum reflection loss of −62 dB at 4.4 GHz, fully cover the whole 5G band of n77, n78, and n79. Simultaneously, it achieves a remarkable through‐plane thermal conductivity of 1.24 W·m −1 ·K −1 and an in‐plane of 3.38 W·m −1 ·K −1 . This work provides a rational design pathway for developing advanced low‐frequency EWA materials with integrated thermal management for 5G applications.