Experimental Observation of Magnetic Surface Polaritons in FeF2by Attenuated Total Reflection

We present the first direct experimental evidence for the existence of magnetic surface polaritons in a uniaxial antiferromagnet. The modes are excited in Fe${\mathrm{F}}_2$ by attenuated total reflection with the uniaxis along an applied magnetic field $H_0$. The resonance is observed as an attenuation of the reflected intensity as the frequency of the far-infrared beam is scanned. We find nonreciprocity between the $+H_0$ and $-H_0$ spectra as a consequence of the nonreciprocity of the surface polariton modes when $H_0$ is introduced. We also observe broad dips due to the excitation of bulk modes.