Creating traveling waves from standing waves from the gyrotropic paramagnetic properties of Fe$^{3+}$ ions in a high-Q whispering gallery mode sapphire resonator

TL;DR

This study demonstrates how the gyrotropic properties of Fe$^{3+}$ ions in a sapphire resonator can convert standing waves into traveling waves, revealing magnetic susceptibility changes at microwave frequencies.

Contribution

It presents the first observation of gyrotropic-induced wave transformation in a high-Q sapphire resonator using Fe$^{3+}$ ions at cryogenic temperatures.

Findings

Standing waves transformed into traveling waves due to gyrotropy.

Magnetic susceptibility change observed at 12.037 GHz.

High-Q whispering gallery mode resonator used for precise measurements.

Abstract

We report observations of the gyrotropic change in magnetic susceptibility of the Fe$^{3+}$ electron paramagnetic resonance at 12.037GHz (between spin states $|1/2>$ and $|3/2>$) in sapphire with respect to applied magnetic field. Measurements were made by observing the response of the high-Q Whispering Gallery doublet (WGH$_{\pm17,0,0}$) in a Hemex sapphire resonator cooled to 5 K. The doublets initially existed as standing waves at zero field and were transformed to traveling waves due to the gyrotropic response.