Abstract
The effect of the external magnetic field on the millimeter‐wave absorption of rhodium‐substituted epsilon iron oxide, ε‐Rh0.13Fe1.87O3 (1) and ε‐Rh0.19Fe1.81O3 (2) nanomagnets, is investigated. Terahertz time‐domain spectroscopy (THz‐TDS) shows that 1 and 2 display a zero‐field ferromagnetic resonance (the so‐called natural resonance) at 201 GHz with a linewidth of 20 GHz and at 210 GHz with a linewidth of 30 GHz, respectively. The ferromagnetic resonance is measured under an external magnetic field (H ex). Applying +3.5 kOe parallel to the remnant magnetization and −3.5 kOe antiparallel to the remnant magnetization shifts the resonance frequency at 201 GHz in 1 by +6 and −4 GHz and that in 2 by +4 and −4 GHz, respectively. Simulations of the ferromagnetic resonance using the Landau−Lifshitz−Gilbert model reproduce the magnetic field‐induced shifts of the resonance frequencies. The 220 GHz band millimeter wave is the highest frequency with a high transparency for “atmospheric windows” and is expected to be a carrier frequency for sixth‐generation mobile communication systems (6 G) or 7 G. This study may help realize applications for millimeter‐wave isolators, circulators, or shutters.
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