Coherent precession of magnetization in superfluid

The coherent precession in bulk He A-phase is unstable due to the positive feedback of spin supercurrent to the gradient of phase of precession. It was predicted that the homogeneous precession will be stable if the orbital momentum could be oriented along the magnetic field. [7] We have found that the orbital part of order parameter in He A-phase immersed in aerogel orients along the direction of aerogel axial squeezing. By this method we have oriented the orbital momentum of He A-phase along the magnetic field and studied non-linear NMR properties. By cw-NMR we have succeeded to form the state with Coherent Precession in He A-phase (CP-A), which is analog of Homogeneous Precession Domain (HPD) in He Bphase. We have found that the dissipation of CP-A and HPD in aerogel is much larger than in bulk superfluid He and depends from sample to sample. We propose a model to explain enhancement of the dissipation in CP-A, which takes into account the spin diffusion of inhomogeneous magnetization created by fluctuations of the condensation energy of Cooper pair in aerogel.