NONLINEAR STATIONARY SPIN-WAVES IN SUPERFLUID HE-3-B AT ULTRA-LOW TEMPERATURES

We have performed detailed CW NMR measurements on superfluid He-3-B in order to investigate stationary spin-wave modes in a texture veil. Ou r results at high temperatures are consistent with previous work. Howe ver, we find that the spin dynamics is profoundly modified, even for s mall excitation amplitudes, for temperatures on the order of 200 mu K, substantially lower than the limit reached in previous investigations . We report the observation of nea-linear spin-waves at ultra-low temp eratures and their characterization in terms of a third-order anharmon ic oscillator.