Magnetic Field Modulated Self‐Assembly of Spherical Carbonyl Iron Particles toward Boosted Electromagnetic Losses for Broadband Microwave Absorption

ABSTRACT Although carbonyl iron (CI)‐loaded magnetic composites are widely recognized for their excellent microwave attenuation at thin thickness, achieving broadband absorption remains challenging. Herein, a magnetic‐field‐assisted self‐assembly strategy is proposed to introduce uniform, long‐range alignments of spherical CI particles in the composites. Compared with composites containing randomly distributed or uniaxially aligned particles, composites with planar alignment (CI‐PA) exhibit markedly enhanced electromagnetic (EM) loss across 2–18 GHz, with dielectric and magnetic losses increased by approximately 5.9 and 1.9 fold, respectively. As a result, the CI‐PA composite reaches a large effective absorption bandwidth (EAB) of 6.43 GHz at an optimal thickness of 1.7 mm, while the minimum reflection loss (RL min ) of −71.62 dB is achieved at a thickness of 3.7 mm at 4.75 GHz, which is rarely achieved in conventional counterparts. Numerical simulation reveals strong field localization and an order‐of‐magnitude enhancement in power dissipation, explaining the improved absorption. Furthermore, a simulated metallic enclosure with an opening aperture demonstrates effective suppression of EM noise and superior shielding effectiveness (SE) in the whole band after applying CI‐PA, demonstrating its great potential for electromagnetic capability (EMC) of compact electronics. This work demonstrates a cost‐effective yet efficient architecture‐driven strategy for developing lightweight, thin, and broadband magnetic microwave absorbers.