No simple antiferromagnetism for ${\mathrm{He}}^3$

If you squeeze helium‐three along its melting curve, the temperature of the liquid–solid system drops. This unusual but well established cooling occurs because the transition from liquid to solid is, in this case, a change from an ordered to a disordered state; the liquid is a spin‐ordered Fermi liquid, with low entropy, whereas the solid, which has many degrees of freedom, is a highentropy state. Theorists predicted that, if compressive cooling were carried down to low enough temperatures, about 2.1 mK, a spin‐ordering transition would occur in the solid, and it would become a nuclear antiferromagnet. But some recent observations at Cornell indicate that the behavior of He3 is much more complicated than had been anticipated: The experiments, in which temperatures low enough to order the nuclear spins were reached for the first time, show not one but two transitions, and the evidence goes against the existence of a simple antiferromagnetic phase.

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