NONLINEAR SPIN DYNAMICS IN U2D2 PHASE OF NUCLEAR ORDERED SOLID HE-3

Pulsed NMR experiments have been performed on monodomain U2D2 solid He-3 in high magnetic fields. It was found that the frequency of the free induction signal changed with time, and in some cases a negative frequency shift as large as 20 kHz from the Larmor frequency was observed. The precession frequency immediately following the rf pulse agreed with Namaizawa's theory, however the free induction signal decayed rapidly. We attribute this to the instability of the uniform precession due to the creation of spin waves, but find disagreement with the instability criterion predicted by Ohmi et al. and Shopova.