First Study of Nuclear Antiferromagnetism by Neutron Diffraction

Antiferromagnetic structures of nuclear spins of ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ and ${}_{}{}^1{}_{}{}^{}\mathrm{H}$ have been produced in a single crystal of lithium hydride by the now standard method of dynamic nuclear polarization followed by an adiabatic demagnetization in the rotating frame (ADRF). The (110) Bragg reflection, characteristic of an antiferromagnetic superstructure, has been observed by neutron diffraction. Its line shape and linewidth have been measured, and the sublattice polarizations studied as a function of variables related to the energy and the entropy of the nuclear spins.