A Millimeter-Wave Absorber Based on Gallium-Substituted epsilon-Iron Oxide Nanomagnets

摘要

Electromagnetic (EM) waves in the millimeter wave range (30-300 GHz) are beginning to be used in electronic devices for high-speed wireless communication such as in local-area networks and radars for the distance between cars. Particularly, millimeter waves at frequencies of 35,94, and 140 GHz have high transparency in the air (the so-called window of the air) and are useful for wireless communication. The development of complementary metal oxide semiconductor devices has also accelerated the use of EM waves in these bands. However, currently materials that effectively restrain electromagnetic interference (EMI) in the region of millimeter waves almost do not exist. Thus, finding a suitable material has received much attention. Insulating magnetic materials absorb EM waves owing to ferromagnetic resonance. Particularly, a magnetic material with a large coercive field (H_c) is expected to show a high-frequency resonance. In recent years, a single phase of epsilon-Fe2O3 nanomagnet has been isolated. This nanomagnet has an extremely large H_c value of 20 kOe at room temperature. Herein, we report a new EM absorber composed of epsilon-Ga_xFe_(2-x)O3 (0.10 <= x <= 0.67) nanomagnets, which shows a ferromagnetic resonance in the region of 35-147 GHz. In addition, the possibility that the ferromagnetic resonance can achieve a frequency of about 190 GHz at x->0 is also suggested.