Susceptibility and pressure study of 3He nano-clusters

Simultaneous measurements of pressure and magnetic susceptibility have been made in He-3 nano-clusters embedded in a He-4 matrix, following phase separation of the mixture. Susceptibility measurements extend from 0.5 mK to 10 mK for three different samples, which either undergo partial melting upon further cooling, or separate with liquid already present. The magnetic behavior of the clusters indicates solid fractions of 77, 54, and 19%, respectively, for pressures of 3.36 MPa, 3.06 MPa, and 2.88 MPa. The susceptibility of the 3.36 MPa sample follows a Curie law to the lowest temperature. For 3.06 MPa, we observe a kink in chi at 1.1 mK, which is approximately the ordering temperature T-N of the pure bulk He-3 if it existed at this pressure. However chi is almost constant down to 0.6 mK, with no drop at 1.1 mK, and no frequency shift, within our resolution of similar to 10 Hz. Thus if there is magnetic odering at 1.1 mK it is quite different than for bulk He-3, not the U2D2 phase. For 2.88 MPa, chi follows a Curie- Weiss law with a positive Weiss theta = 140 muK, indicative of a ferromagnetic tendency, similar to that seen in 2D films.