Nuclear magnetic ordering in solid 3He (invited)

Abstract

Solid 3He is the most quantum mechanical of the inert gas solids. In the bcc solid close to the melting pressure, 3He atoms exchange lattice sites with their neighbors millions of times each second, thereby reducing their zero point energy. This atom-atom exchange leads to a spin exchange energy in the solid which is nearly ten thousand times larger than the dipole-dipole energy between neighboring 3He atoms, and as a result, nuclear antiferromagnetism in solid 3He occurs at the unusually high temperature of about 0.001 K. This temperature can be produced directly with modern refrigeration techniques, and recent experimental studies have given us our first detailed picture of the resulting antiferromagnetic states. In magnetic fields below 4 kOe a highly anisotropic sublattice structure with a [100] symmetry is found. Above 4 kOe, a very different structure is observed with apparent cubic symmetry and a nearly field-independent magnetization, which is about 60% of the saturation magnetization. Although the exchange Hamiltonian for this system cannot be determined from first principles, modern multiple exchange theories appear capable of predicting many of the observed features.