Evidence for ferromagnetic order in the boundary layer ofHe3on graphite

Recent measurements of the surface magnetism of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ on graphite show that the surface susceptibility ${\chi }_s$ in a magnetic field would increase rapidly at temperatures below the temperature estimated for a ferromagnetic transition if the applied magnetic field were zero. An anisotropic frequency shift develops at low temperatures and is consistent with the magnetization coming from a two-dimensional sheet of spins. A low-temperature decrease in the spin-spin relaxation time gives another indication of the two-dimensional character of this system.