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

Abstract

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\ifmmode^\circ\else\textdegree\fi{}K. The temperature variation of the Young moduli $E$, shear moduli $G$, adiabatic compressibilities ${K}_{s}$, Debye temperatures ${\ensuremath{\Theta}}_{D}$, and ultrasonic attenuations have been determined. The anomalies in the elastic and anelastic properties, observed at temperatures below 25\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K). In contrast, Pr and Sm display maxima at 78 and 109\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}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.