Parametric instability of homogeneous precession of spin in the   superfluid 3He-B
  Stability of homogeneous precession of spin due to parametric excitation of spin waves is considered as the explanation of the "catastrophic relaxation", that is observed in the superfluid 3He-B. It is shown, that at sufficiently low temperatures homogeneous precession of spin becomes unstable (Suhl instability). At zero temperature increments of growth for all spin wave modes are found. Estimation of the temperature of transition to the unstable state is made. 
E.V. Surovtsev, I.A. Fomin