Spin-wave velocity, entropy, and magnetization in bcc solidHe3

Precise measurements of the ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ melting pressure in several magnetic fields have been made through the various magnetic ordering transitions. Throughout the low-field phase, we find a ${\mathit{T}}^4$ temperature dependence of the melting pressure, characteristic of antiferromagnetic spin waves with linear dispersion and a velocity of 7.8 cm/s, almost independent of field. However, the melting pressure in the high-field phase (HFP) deviates from the ${\mathit{T}}^4$ dependence near the HFP-paramagnetic phase transition, resulting in a very rapid entropy change near ${\mathit{T}}_{\mathit{c}}$. The spin-wave velocity increases with field, consistent with a strong temperature dependence of the magnetization. The entropy and magnetization discontinuities across the various phase boundaries have been determined. All results are thermodynamically consistent with the measured magnetic phase diagram.