Spin echoes and diffusion in normal-fluid He-3

Nonlinear spin dynamics in a bulk fluid He-3 sample at 0 bar were investiga ted in pulsed NMR experiments at temperatures of 5-150 mK in field gradient s 1-7 mT/cm at a frequency of 26.4 MHz in order to elucidate the influence of a high molecular field parameter mu M similar to 136/T-2 [mK] on spin di ffusion. Multiple Spin Echo amplitudes were monitored and analyzed after th e application of a pi/2 - tau - pi/2 pulse sequence. For the time dependenc e of the first echo amplitude, the typical exp(- t(3)) decay was only found for small effective diffusion coefficients. In addition, neither numerical simulations nor analytic approximations to Leggetts equations for the prec ession of spin currents around the local molecular field could explain the observed time evolution of the MSE-structure. (C) 2000 Elsevier Science B.V . All rights reserved.