Elastic Moduli and Ultrasonic Attenuation of Praseodymium, Neodymium, and Samarium from 4.2 to 300°K

The LA and TA wave velocities and the ultrasonic attenuations of high-purity polycrystalline Pr, Nd, and Sm have been measured by a pulse technique at a frequency of 10 MHz between 4.2 and 300^∘{}K. The temperature variation of the Young moduli E, shear moduli G, adiabatic compressibilities Kₛ, Debye temperatures ΘD, and ultrasonic attenuations have been determined. The anomalies in the elastic and anelastic properties, observed at temperatures below 25^∘{}K, were correlated with the antiferromagnetic transitions known to occur in these metals. The elastic moduli of Nd behave in a normal manner between room temperature and its N\'eel point (18^∘{}K). In contrast, Pr and Sm display maxima at 78 and 109^∘{}K, respectively, followed by a sharp decrease in the elastic moduli with decreasing temperature, i.e., the appearance of a lattice-softening phenomenon. Noteworthy is the similarity in the temperature variation of the elastic moduli and ultrasonic attenuations between Pr and Sm. The anomalies at 78 and 109^∘{}K, in these metals, are believed to be due to an electron-type transition or to a crystallographic phase change rather than to an antiferromagnetic ordering.