Sound velocity measurement of nuclear-ordered U2D2 solid He-3 along the melting curve

The sound velocity of a single-domain He-3 crystal was measured in the nucl ear-ordered low-held phase and the paramagnetic phase along the melting cur ve, using 10.98 MHz longitudinal sound. The temperature dependence of the s ound velocity along the melting curve was explained by a nuclear spin contr ibution and the molar volume change along the melting curve. By comparing t he measured velocity with thermodynamic quantities, we extracted the Grunei zen constant for the exchange energy. The anisotropy of the velocity in the ordered phase was investigated for three samples and was found to be small er than 2 x 10(-5) in Delta nu/nu. The attenuation coefficient of the sound was much smaller than 0.2 cm(-1). (C) 2000 Elsevier Science B.V. All right s reserved.