Ultrasonic Attenuation near the Critical Point of MnF2

Ultrasonic attenuation and velocity have been measured in MnF₂ in the vicinity of the Néel temperature. Longitudinal and transverse waves were propagated in the [110] and [001] directions. Peaks in the attenuation for longitudinal waves were observed for both directions of propagation. Both peaks occur at the Néel temperature and no velocity change at this temperature was observed for any mode of propagation. The data are in qualitative agreement with recent calculations.