Ultrasonic Studies of Antiferromagnetic Resonance in RbMnF3near the Néel Temperature

Peaks found in the attenuation of transverse and longitudinal ultrasonic waves in RbMn${\mathrm{F}}_3$ below the Néel temperature are identified as due to antiferromagnetic resonance on the basis of their temperature-frequency relation and magnetic field dependence. The temperature dependence of antiferromagnetic resonance has thus been determined for $0.1°\mathrm{K}\lesssim T_{\mathrm{N}}-T\lesssim 4°\mathrm{K}$, where $T_{\mathrm{N}}$ is the Néel temperature.