Surface-Spin-Induced Magnetic Loss Enhancement in Ultralight Electromagnetic Absorbers

Limited by the intrinsic magnetic loss ability, the electromagnetic wave absorption (EMA) materials have encountered a bottleneck to achieve effective EMA with super-low density. In this work, we propose a novel strategy to boost magnetic loss capacity by controlling surface atom spin. Using hollow Fe₃O₄ nanoparticles as a model, with their hollow rates controlled to 0, 17.1%, 32.2%, 46.6% and 54.1%, we reveal that the magnetic loss capacity is mainly dependent on the surface atom moment rather than the body moment. Attributed to the coexistence of inside and outside surface atoms moment, the 54.1% hollow Fe₃O₄ absorber represents about 20% enhancement in the imaginary part (µ'') than solid particles over 2-18 GHz. This improvement further makes the effective absorption bandwidth (≤-5 dB) at 2.0 mm broaden to 11.91 GHz from 5.68 GHz in solid Fe₃O₄ nanoparticles and makes the absorption ability shift to low frequency. More importantly, the density of 54.1% hollow Fe₃O₄ absorber is only 48.9% of solid sample, which is very promising to meet the requirements for miniaturization and lightweighting. These findings provide important theoretical and practical guidelines for designing ultralight magnetic absorbers.