Abstract
Ultrasonic attenuation in KMnF3 has been measured at frequencies ranging from 10-170 MHz near 186-2K. The frequency and temperature dependences of the critical attenuation are determined and the dynamic scaling hypothesis is examined. Above 186-2K, it is found that the critical attenuation alpha is described by a scaling function, alpha = omega yF( omega / Omega kappa ), where y=0.13+or-0.05 and Omega kappa is the characteristic frequency of the order parameter fluctuation with the wave number equal to the inverse correlation length. The temperature dependence of Omega kappa is discussed in the light of the Murata's (1976) theory for the sound attenuation of the perovskite crystal near the structural phase transition point.