Particle size effect on millimeter-wave absorption, rotation, and ellipticity of gallium-substituted epsilon iron oxide

Various applications employ millimeter waves. For example, the carrier frequencies of vehicle radar in advanced driver assistance systems are 76-81 GHz millimeter waves. Here, we investigate the particle size effect on millimeter-wave absorption of gallium-substituted epsilon iron oxide epsilon-GaxFe2-xO3 with x = 0.44 +/- 0.01. Samples were composed of nanoparticles with sizes of 16.9(1) nm, 28.8(2) nm, and 41.4(1) nm. Millimeter wave absorption, Faraday rotation, and Faraday ellipticity were measured by terahertz time-domain spectroscopy. This series exhibits millimeter-wave absorption at 78.7, 78.2, and 77.7 GHz without an external magnetic field. The millimeter-wave absorption increases from 4.6 dB to 9.4 dB as the particle size increases. In the magnetized sample, the Faraday rotation angle increases from 9.1 degrees to 18.4 degrees, while the Faraday ellipticity increases from 0.27 to 0.52. The particle size effect can be explained by the change in the ratio of the surface and core of the nanoparticles. The present study should contribute to the realization of high-performance millimeter-wave absorbers.

Automated summary

This study investigates the particle size effect on millimeter-wave absorption of gallium-substituted epsilon iron oxide. The results show that as the particle size increases, the millimeter-wave absorption and Faraday rotation increase, indicating a significant influence of particle size on millimeter-wave absorption.