Elastic Moduli and Ultrasonic Attenuation of Polycrystallineα−Mnfrom 4.2-300°K

Abstract

The longitudinal and transverse acoustic velocities and the ultrasonic attenuation of high-purity polycrystalline $\alpha -\mathrm{M}\mathrm{n}$ have been measured by an ultrasonic pulse technique between 4.2 and 300°K. The variations with temperature of the Young's modulus $E$, adiabatic compressibility $K_s$, and Debye temperature ${\Theta }_D$ have been determined. The Néel point, 96°K, is marked by drastic changes in the elastic moduli. The behavior of the ultrasonic attenuation in the vicinity of the Néel point is in qualitative agreement with the Landau-Khalatnikov theory. A subsidiary peak, probably related to short-range ordered clusters, was observed at about 175°K. The limiting value of ${\Theta }_D$ is 485°K.