MULTIPLE SPIN ECHOES IN SPIN-POLARIZED FERMI LIQUIDS

Multiple spin echoes (MSEs) in He-3 and in He-3-He-4 mixtures have been analyzed using a theoretical technique proposed by Einzel et al. In both systems MSEs are generated by Fermi liquid interactions, but for He-3, MSEs are also generated at higher temperatures by the dipolar demagnetizing field. The theory is compared with the experimental results for He-3 and with our measurements for He-3-He-4 mixtures. We have improved on the fit to the second echo heights for He-3 given by Einzel et al. by taking account of both the Leggett-Rice effect and the dipolar interaction in the calculation. Good fits were also found for the first and second echo heights for the He-3-He-4 data. The third echo height is larger than expected if we assume that the total magnetization remains uniform in space. We have developed the theory for the case when this approximation is not made, and we find good agreement for the first five echoes.