Sound Velocity Measurements of Nuclear‐Ordered Solid 3He in the Low Field Phase

We have measured, along the melting curve, the magnetic‐field dependences of the velocities of the longitudinal and two transverse sound modes in the low field phase (U2D2) of nuclear‐ordered solid 3He crystals with a single magnetic domain. We determined the elastic‐stiffness tensors cij(T,B) along the melting curve at T=0.5 mK. Since the U2D2 phase has a tetragonal symmetry, we extracted six components of the nuclear‐spin elastic‐stiffnesses tensor Δc ijN(0.5 mK,B). We obtained the generalized Gruneisen constants Γij1/χ for the magnetic susceptibility χ from ΔcijN(0.5 mK,B), which were proportional to B2.