Microwave Absorption Properties of Iron Nanoparticles Prepared by Ball-Milling

A nanopowder of iron was prepared using a high-energy ball milling method, which is capable of producing nanoparticles at a reasonably larger scale compared to conventional chemical methods. Analyses using x-ray diffraction and magnetic measurements indicate that the iron nanoparticles are a single phase of a body-centered cubic structure and have quite stable magnetic characteristics in the air. The iron nanoparticles were then mixed with paraffin and pressed into flat square plates for free-space microwave transmission and reflection measurements in the 4-8 GHz range. Without an Al backing plate, the Fe nanoparticles seem to only weakly absorb microwave radiation. The reflected signal S (11) drops to zero and a very large negative value of reflection loss (RL) are observed for Al-backed samples, suggesting the existence of a phase matching resonance near frequency f 6 GHz.