Nuclear magnetic properties ofHe3adsorbed on graphite

Precise measurements are presented for the nuclear susceptibility of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ films adsorbed on exfoliated graphite at millikelvin temperatures as a function of coverage (0.53–1.42 layers). Ferromagnetic Curie-Weiss temperatures are determined above and below the perfectly commensurate coverage. In the incommensurate phase, the effective exchange interactions are found to be much smaller than those determined by heat capacity, suggesting a strong departure from a Heisenberg Hamiltonian description. The evolution of the NMR line shape as a function of coverage disagrees with previous data in the incommensurate phase and around monolayer completion. The dependence of the Curie constant on coverage is consistent with recent neutron-scattering results, suggesting an interpretation of the phase diagram and a modified coverage scale. We also present a description of the techniques developed in our laboratory which allow performing surface physics experiments at millikelvin temperatures.