Attenuation of High-Frequency Acoustic Waves on the Low-Temperature Side of the MnF2Néel Point

We present acoustic-attenuation experiments at frequencies up to 1000 MHz in the vicinity of the Néel point of Mn${\mathrm{F}}_2$. They show that the attenuation is maximum in the low-temperature phase near the transition, and the temperature at which that maximum appears decreases as the frequency increases. A brief scanning of the theory is given which explains this new effect in terms of relaxation of staggered magnetization.