The presence of a magnetized element, say, a ferrite, or a magnetically biased plasmonic particle in a guiding medium leads to nonreciprocal behavior of the entire ambient surroundings. The nonreciprocity measure depends on the particle's excitation, which in turn depends on the magnetized material damping rate $\mathrm{\Gamma }$. Therefore, intuitively speaking, the heavier the material damping rate is, the weaker the nonreciprocal response. In this Letter, we reveal a more delicate mechanism demonstrating a loss-threshold phenomenon for nonreciprocity. Specifically, under certain conditions, we show that the nonreciprocity effect is robust against material loss up to a critical loss threshold ${\mathrm{\Gamma }}_{\mathrm{c}}$ that depends on the magnetization bias strength. Although this effect can be observed to some limited extent in the near field of the magnetized element, even in free space, its appearance when the magnetized particle is placed inside a cavity, as is often the case in nonreciprocal microwave devices, is substantially stronger and occurs with magnetization strength equivalent to cyclotron over plasma frequency as low as 5%–10% and with loss rates in the same order, thus making it measurable in various configurations and a wide range of frequencies from rf to low terahertz.

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• Non-reciprocal propagation
• Complex media
• Polarizability
• Cavity methods
• Green's function methods
• Threshold & cascade models