Sound velocity and attenuation in nuclear-ordered U2D2 solid 3He

We studied sound properties of nuclear-ordered U2D2 solid 3He crystal with a single magnetic domain along the melting curve. We measured temperature dependences of sound velocities and attenuations for a longitudinal and two transverse sounds between the sound frequency f, 3 and 50 MHz below the nuclear-ordered transition temperature TN. The sound velocity v changes as Δv/v=a(T/TN)4 and the attenuation α approximately as Δα=cf3(T/TN)9. The coefficients a and c depend on crystal orientations and sound modes. Assuming the tetragonal symmetry of U2D2 crystal, we determined six independent elastic constants of nuclear spin system from Δv/v