Susceptibility and Pressure Study of 3He nano-Clusters

Abstract

Simultaneous measurements of pressure and magnetic susceptibility have been made in ³He nano-clusters embedded in a ⁴He 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 χ at 1.1 mK, which is approximately the ordering temperature T_N of the pure bulk ³He if it existed at this pressure. However χ is almost constant down to 0.6 mK, with no drop at 1.1 mK, and no frequency shift, within our resolution of ∼10 Hz. Thus if there is magnetic ordering at 1.1 mK it is quite different than for bulk ³He, not the U2D2 phase. For 2.88 MPa, χ follows a Curie-Weiss law with a positive Weiss θ=140 μK, indicative of a ferromagnetic tendency, similar to that seen in 2D films.