Nonlinear longitudinal NMR in superfluid 3He

The effect of a strong magnetic field on the relative orientation of the field, average spin, and order parameter vectors is considered for longitudinal NMR in superfluid 3He. It is shown that the orientation is stabilized by strong static fields. Resonant effects are considered for nonlinear parallel ''ringing'' in which there is a slow broadening or stochastic modulation of the ringing frequency. The angle orientation is shown to be stable for the A phase, but in the B phase the stability depends on the remanent static field after the nonlinear ringing has been excited