Free-Induction-Decay Shapes in a Dipolar-Coupled Rigid Lattice of Infinite Nuclear Spins

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Abstract
A molecular-dynamics experiment is used to derive free-induction-decay curves for a rigid cubic lattice with 216 classical spins coupled by magnetic dipole interaction. Free-induction-decay curves are obtained for the magnetic field along the [100], [110], and [111] axes of the lattice. The shapes of these curves are compared to the shapes derived from the expansion theory of Gade and Lowe and to the shapes based on Abragam's trial function. A considerable difference is found between the predictions of the Gade and Lowe theory and our experiments, whereas Abragam's trial functions reproduce the experiments quite well except for long times. Continuous-wave spectra obtained by Fourier transformation of the free-induction-decay curves are also reported as well as their first few moments. The moments are in good agreement with the second and fourth moments given by Van Vleck.