Fun games to play with your spin waves:
A. J. Leggett and M. J. Rice
"Spin Echoes in Liquid He3 and Mixtures: A Predicted New Effect"
Phys. Rev. Lett. 20, 586–589 (1968) http://prl.aps.org/abstract/PRL/v20/i12/p586_1
Google Scholar can find lots more...................