The sound velocity measurements of nuclear-ordered bcc solid 3He under magnetic fields

We measured the sound velocity of nuclear-ordered bcc solid 3He in the low field phase (U2D2), and the high field phase (CNAF) along the melting curve. Previously we reported a temperature dependence of the sound velocity in a single magnetic domain of U2D2 3He at almost zero fields. We extended this measurement and obtained a field dependence in both the U2D2 and the CNAF phases to further investigate the nuclear magnetism of nuclear-ordered bcc solid 3He by using the multiple-spin ring exchange model. The sound velocity varied as B2 in the U2D2 phase and had a large jump at the phase transition, and then gradually increased as field increased in the CNAF phase. These results are attributed to the nuclear-spin part of the internal energy.