Critical dynamics at the structural transition of KMnF3from ultrasonic experiments

Abstract
From the measurement of the frequency dependence of the ultrasonic attenuation coefficient for the longitudinal wave in KMnF3, the width of the central peak is obtained by applying extended Schwabl's theory (1973). This central peak shows a critical slowing-down, and its width is about 20 MHz at T=Tc+1K and about 170 MHz at T=Tc+4K.