Solution of the problem of catastrophic relaxation of homogeneous spin precession in superfluid 3He-B

The quantitative analysis of the "catastrophic relaxation" of the coherent spin precession in He-3-B is presented. This phenomenon has been observed below a temperature of about 0.5 T-c as an abrupt shortening of the induction signal decay. It is explained in terms of the decay instability of the homogeneous transverse NMR mode into spin waves of the longitudinal NMR. Recently, the cross interaction amplitude between the two modes has been calculated by Sourovtsev and Fomin [9] for the so-called Brinkman-Smith configuration, i.e., for the orientation of the orbital momentum of Cooper pairs along the magnetic field, L parallel to H. In their treatment, the interaction is caused by the anisotropy of the speed of the spin waves. We found that, in the more general case of the nonparallel orientation of L corresponding to the typical conditions of the experiment, the spin-orbital interaction provides the additional interaction between the modes. By analyzing the experimental data, we are able to distinguish which contribution is dominating in different regimes.