Spin dynamics and onset of Suhl instability in bcc solid3He in the nuclear-ordered U2D2 phase

Abstract

Pulsed NMR experiments have been performed on U2D2 solid3He with a single domain in high fields where the Larmor frequency was much larger than the zero-field antiferromagnetic resonance frequency. The free induction signal decayed rapidly under certain conditions. The rapid decay is attributed to the onset of the instability of the uniform precession. We propose a model for the instability due to the self-induced emission from the upper-mode magnon to the lower-mode magnon which is similar to the Suhl instability in electronic ferromagnets. A large negative frequency shift was observed during the rapid decay, which is consistently explained by the model. Under stable conditions of the spin motion outside of the instability region, we observed the tipping-angle-dependent frequency shift and multiple spin echoes, both of which agree well with Namaizawa's theory.