Strong coupling antiferromagnetic resonance with sub-THz cavity fields

Strong coupling of electromagnetic cavity fields with antiferromagnetic spin waves in hematite ($\alpha$-Fe${}_2$O${}_3$) was achieved above room temperature. A cube of hematite was placed in a metallic tube and transmission was measured, using a continuous-wave THz spectrometer. Spectra, collected as a function of temperature, reveal the formation of magnetic polaritons.