ε-Iron Oxide Exhibiting High-Frequency Millimeter Wave Absorption

Abstract

This review article describes the large coercive field and high frequency millimeter wave absorption of ε-Fe₂O₃. In 2004, we obtained pure ε-Fe₂O₃ phase by a particular chemical synthesis method for nanosize particles, a combination method of reverse-micelle and sol-gel techniques. This ε-Fe₂O₃ exhibits a huge coercive field of 20 kOe at room temperature. In addition, its physical properties can be widely controlled by substituting the iron cations with other metal cations. In this paper, the synthesis, crystal structure, magnetic properties, and especially, the millimeter wave absorption properties of ε-Fe₂O₃ and metal substituted ε-Fe₂O₃, ε-M_xFe_2–xO₃ (M=Al and Ga) are presented. ε-Fe₂O₃ and ε-M_xFe_2–xO₃ based magnets have the possibility as millimeter wave absorbers for the future high-speed wireless communications.