Low‐Carbon‐Residue Multi‐Principal‐Element Magnetic Alloys for Excellent Microwave Absorption

Magnetic alloy/carbon composites are promising microwave absorbers due to abundant interfaces and multiple loss mechanisms. However, reducing carbon content while maintaining uniform magnetic component distribution remains challenging. We report a spray‐drying strategy to address this. By tuning nitrate precursor ratios and optimizing thermal treatment, we synthesize low‐carbon alloy/oxide microspheres with uniformly distributed alloy phases. Limiting carbon content improves impedance matching, while selective nitrate precipitation creates a magnetic alloy architecture that suppresses nanoparticle agglomeration and enhances interfacial polarization. For this multiscale synergistic polarization is achieved: highly conductive Cu maximizes conduction loss, insulating Al 2 O 3 buffers impedance, and Mn provides abundant polarization centers. The resulting microspheres exhibit tunable, exceptional performance. The attenuation‐dominated FeCuMn system achieves −48.2 dB minimum reflection loss at 1.5 mm thickness. The impedance‐matched FeCuAl system delivers an ultra‐broad effective absorption bandwidth (EAB) of 5.12 GHz. Additionally, the FeAlMn system demonstrates superior polarization miniaturization for optimal absorption at extremely thin matching thicknesses. This work provides a practical strategy for designing electromagnetic composite structures with tunable component distribution.