Nuclear antiferromagnetic ordering in lithium fluoride

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Abstract
The onset of nuclear antiferromagnetism has been observed in lithium fluoride 7Li19F. The ordering is due to the magnetic-dipole interactions between nuclei so that lithium fluoride becomes the second substance in which such ordering has been sought experimentally, and the first to exhibit an antiferromagnetic state in which two species of nuclear spin participate. The simultaneous cooling of the 7Li and 19F nuclei to a common dipolar temperature below a microdegree, 10-6K, is described in terms of the various thermal reservoirs which make up the spin system. Three different experiments and their results are presented: two concern the measurement of a macroscopic property of the ordered state-its magnetic susceptibility-and the third concerns a microscopic property-the resonance of a nuclear probe. The probable spin configuration of the state is determined using the local Weissfield approximation.