A Millimeter-Wave Tunable Electromagnetic Absorber Based on $\varepsilon$-Al$_{\rm x}$Fe$_{2-{\rm x}}$O$_{3}$ Nanomagnets

Abstract

High-performance millimeter-wave absorber composed of ε-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanomagnets is prepared by sol-gel techniques. Free space quasi-optical spectrometer equipped with a set of tunable backward-wave oscillators as power sources is used in this work to study the absorption property of this series of materials. Special aluminum-disc sample container with thickness of 2 mm is fabricated. Transmittance spectra of ε-Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> with different x values (x = 0.66 and 0.49) are recorded using our free space spectrometer. Strong magnetic absorption at 95 GHz (corresponding to x = 0.66) and 105 GHz (x = 0.49) are found. Combining the data obtained in this and previous work, second order polynomial curve is simulated to study the x parameter dependence of absorption frequencies. The simulation results are in good agreement with the experimental ones.