Nuclear ferromagnetic and antiferromagnetic exchange in thin films of 3He adsorbed on graphite

Measurements of the nuclear magnetic susceptibility of multilayer films of 3He adsorbed on graphite plated with a monolayer of 4He are reported for 3He surface densities up to 0.27 A-2 and temperatures in the range (6/600 mK). The coverage dependence of the exchange constant has been measured; this is antiferromagnetic when the second layer first solidifies and becomes ferromagnetic with the formation of a fluid overlayer. The second-layer solid density evolves in a stepwise fashion with increasing coverage, while the susceptibility of the fluid overlayer shows structure associated with layering in the film