Microwave Absorption in the GHz Range of Nanostructure Produced by Disproportionation Reaction of Rare Earth-Iron Compound

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For the 1-5 GHz frequency range, both Spinel-type ferrites and metallic magnetic materials can be used as electromagnetic wave absorbers. However, because the latter materials have larger values of saturation magnetization, their Snoek's limit are at a higher frequency and so their values of relative complex permeability remain high in this frequency range. Therefore, it is possible to make thinner absorbers from metallic magnetic materials.The magnetization of electrically conductive magnetic materials, induced by electromagnetic waves, decreases due to eddy current losses. For this reason, it is best to use smaller particles, compared to the skindepth, when making electromagnetic wave absorbers from such materials. In this study, the possibility of using the disproportionation reaction of the Sm_2Fe_<17> compound for the production of powders with a fine α-Fe structure was investigated, for use as electromagnetic wave absorbers that can operate in the GHz frequency range. A fine α-Fe … More / SmH_2 or α-Fe / SmO structure with a sub-micrometer size is formed from the Sm_2Fe_<17> compound after disproportionation in hydrogen or air, respectively. In this way, magnetic powders with a fine structure of α-Fe were obtained. The powders disproportionated in hydrogen, were heated in air in order to oxidize the Sm hydride, to give a α-Fe / SmO two-phase microstructure, and thereby increase the resistivity of the powders. Toroidally shaped epoxy-resin composites were made from this powder, and the microwave absorption properties of these samples were measured. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range. However, the disproportionated samples (heated in hydrogen at 873 K for 1 hour, milled for 30 minutes and oxidized at 473 K for 2 hours in air) exhibited electromagnetic wave absorption (R.L.< -20dB) in the frequency (f_m) range 0.73 to 1.30 GHz, for absorber thicknesses (dm) ranging from 13.1 to 7.9 mm, respectively. The disproportionated samples in air (heated at 473K for 2 hours and milled for 30 minutes) also showed good electromagnetic wave absorption properties (f_m=-1.21 - 2.50 GHz and d_m= 8.0 - 4.2 GHz). It is concluded that the disproportionation reaction, in either hydrogen or in air, is a useful method for the production of powders with a fine α-Fe structure, which can be used for microwave absorbers that operate in the several GHz range. Less