A new look at ferromagnetic two-dimensional magnetism of He-3

He-3 films on graphite at densities above 20 atoms/nm(2) have a strong ferr omagnetic tendency. Models of multiple spin exchange are believed to descri be the dominant interaction. However, other much smaller interactions can s ignificantly alter the low-temperature behavior of these systems, especiall y in very low magnetic fields. Our recent experiments have used a SQUID sys tem for both pulsed and continuous wave NMR at very low applied fields (B < 1 mT). Our results show that the polarization of this system grows much mo re rapidly than is expected from the Heisenberg exchange models, even appro aching saturation. Possible explanations are the influence of finite size e ffects and dipolar interactions. (C) 2000 Elsevier Science B.V. All rights reserved.