Electromagnetic Wave Absorption Properties of RE-Fe Nanocomposites

Abstract

Recently, the number of communication devices that utilize gigahertz range microwave radiation, such as mobile phones and LAN systems, has greatly increased. However, electromagnetic interference (EMI) has become serious. One promising technique to prevent EMI is the use of microwave absorption materials. However, the applications of conventional microwave absorption materials are limited. The reasons are that Snoek’s limit of spinel-tripe ferrites is so small that the imaginary part of permeability is considerably lowered in GHz range, and metallic soft-magnet materials have high electric conductivity, which makes the high frequency permeability decreased drastically due to the eddy current loss induced by EM wave. The Nd2Fe14B/-Fe composites is composed of soft magnetic -Fe phase with high MS and hard magnetic Nd2Fe14B phase with large HA, consequently their natural resonance frequency are at a high frequency range and permeability still remains as a large value in high frequency range. Furthermore, the electric resistivity of Nd2Fe14B is higher than that of metallic soft magnetic material, which can restrain the eddy current loss. Thus, the authors have already reported that Nd2Fe14B/-Fe composites can fuction as a microwave absorber. In this present work, the electromagnetic and absorption properties of the Nd2Fe14B/-Fe nanocomposites were studied in the 0.5–18 and 26.5–40 GHz frequency ranges. Moreover, the effect of rare earth Nd content on natural resonance frequency and microwave permeability of Nd2Fe14B/Fe nanocomposites was reported in this chapter. The results show that it is possible to be a good candidate for thinner microwave absorbers in the GHz range. In order to restrain the eddy current loss of metallic soft magnetic material, Sm2O3 and SmN was introduced in Sm2O3/α-Fe and SmN/α-Fe composites as dielectric phase, and Sm2Fe17Nx with high magnetocrystalline anisotropy was introduced in SmN/αFe/Sm2Fe17Nx as hard magnetic phase. Accordingly, Sm2O3/α-Fe and SmN/αFe/Sm2Fe17Nx are possible to be another good candidate for microwave absorbers in the GHz range as the authors reported in reference. Therefore, the purpose of this study is to investigate the microwave complex permeability, resonant frequency, and microwave absorption properties of nanocrystalline rare-earth magnetic composite materials Sm2O3/αFe and SmN/α-Fe/Sm2Fe17Nx. The absorption performance and natural resonance frequency can be controlled by adjusting phase composite proportion and optimizing the microstructure.