Elastic constants of terbium between 78 and 300 K

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Abstract
The adiabatic elastic constants of terbium were determined in the temperature range 78–300 K, using high‐purity single crystals. The constants were obtained from the ultrasonic wave velocities (20 MHz) measured by the pulse‐superposition method. The values of the constants c 33, c 44, c 11, c 12, and c 13 at room temperature in units of 1011 dyn/cm2 are 7.225, 2.140, 6.788, 2.432, and 2.299, respectively. Using these values, the Debye temperature was computed to be 176.6 K. The velocities tend to vary with temperature in an anomalous fashion near the magnetic phase transitions, i.e., the Néel and Curie temperatures, 229 and 221 K, respectively. The relative change of the longitudinal velocity in the [0001] direction, near the Néel temperature,TN , could be described by a logarithmic function of the reduced temperature (T‐TN )/TN . The rate of the relaxation process of this relationship was estimated to be 6×109 sec−1.