THE FORMATION AND MELTING OF HE-3 CLUSTERS IN PHASE-SEPARATED SOLID HE-3-HE-4 MIXTURES

Melting pressure measurements have been made on the He-3-rich phase fo rmed by cooling a solid mixture of 0.6% He-3 in He-4 through phase sep aration, at pressures between 2.78 and 3.56 MPa. For comparison, simul taneous observations were made with the mixture confined in the pores of a silver sinter and in an open volume connected to the same fill-li ne. Samples in the sinter cell solidify at higher pressures than the o pen cell and equilibrate more quickly. Both cells exhibit hysteresis b etween melting and freezing temperatures, and the transitions are broa der in the open-volume cell. Relative to pure He-3, the melting pressu re is elevated by as much as 60 kPa in the sinter cell and 20 kPa in t he open cell. The size of the pressure change on melting indicates tha t a large fraction of the He-3 remains solid at pressures below the me lting curve, and this effect is more pronounced in the sinter cell. Me asurements are in progress to measure the magnetisation through the ma gnetic ordering transition.