SQUID NMR studies of the dipole field in ferromagnetic 3He films

We use SQUID NMR to observe the magnetization of He-3 films with densities between 20 and 24 atoms/nm(2) in the zero field limit. Ferromagnetism in these nearly 2D Heisenberg exchange systems is stabilized by weak anisotropies. In the ferromagnetic phase, the NMR line becomes very broad and shifts to lower frequencies, consistent with a large dipolar field opposing a perpendicular applied field. Grafoil can be modeled by a Gaussian distribution of platelet angles centered on the normal to the Grafoil plus a randomly distributed set of platelets. Using the spin dynamics of a 2D polarized sheet with reasonable assumptions for the distributions of platelet angles, we show that the magnetization, frequency shift and line shape form a consistent picture of a highly polarized sheet. (C) 2002 Elsevier Science B.V. All rights reserved.