Spin dynamics of 3He in aerogel

We report continuous-wave NMR measurements on superfluid(3) He contained inside high porosity aerogel at 3.24 MPa, in a 28.4 mT magnetic field, and down to 0.9 mK. Three different purities of He-3 were used: pure He-3, He-3 with enough He-4 to replace the first localized layer, and He-3 with enough He-4 to replace both localized layers. Below 2.26mK, the NMR spectrum does not consist of a single Lorentzian, but a distribution of NMR resonant frequencies both above and below the Larmor frequency, wt. Upon cooling, the component of the spectrum at frequencies below the Larmor frequency moves to higher frequencies over a narrow temperature range and does not return to w < w(L) upon warming. The higher frequency component of the spectrum displays two resolvable peaks which become a complex structure upon removal of the localized He-3 spins. The spectrum changes as the magnetic field is rotated about the axis of the aerogel sample, indicating that the 3He is able to detect a preferred direction in the aerogel. The shape of the spectrum shows no rotation or magnetic field hysteresis. We find that the average frequency shifts of our NMR spectra do not depend on the presence of the localized 3He spins. These frequency shifts and the presence of a temperature-independent magnetization for the liquid 3He suggest that the aerogel stabilizes a single equal-spin-pairing state in our experiments.