Growth of third ferromagnetic solid 3He layer on graphite with and without 4He pre-plating

We have measured the nuclear susceptibility of 3He in Grafoil filled with pure liquid 3He over the pressure region between 0.6 and 31.38 bar and at temperatures down to 0.5 mK with a cw NMR method. The nuclear magnetization corresponding to the adsorbed 3He layers on the Grafoil surface shows a strong ferromagnetic tendency with a periodic behavior as a function of liquid pressure. This observation is attributable to the growth of third and fourth solid 3He layer with the liquid pressure increase. The pressure dependence of the Weiss temperature indicates that the third layer is completed at 19 bar and the fourth probably at 28 bar. The results for Grafoil pre-plated by 2.5 and 3.5 layers of 4He are consistent with this scenario.