Abstract
Recent measurements of the spin-wave dispersion relations for Gd, Dy, and Ho metal by triple-axis neutron spectrometry will be reviewed. Measurements along the c axis have been carried out for each metal at several temperatures, and for Gd additional measurements along the a and b axes have been made at 78°K. Information about the Fourier-transformed exchange interaction J(q) has been obtained from data analyses, which are based on a simple Hamiltonian containing only exchange interactions for Gd and a Hamiltonian containing exchange interactions plus appropriate anisotropy interactions (the usual frozen lattice model) for Dy and Ho. For both Dy and Ho a satisfactory analysis of the data requires the use of anisotropy interaction parameters which are not in good agreement with the results of macroscopic measurements. The neutron data suggest the existence of other anisotropy interactions, perhaps magnetoelastic, in addition to those usually considered in the frozen lattice Hamiltonian. The dispersion relation for Dy in the ferromagnetic phase has a pronounced minimum, and hence J(q) has a maximum, for q in the vicinity of the wave vector that is appropriate for the spiral structure just above Tc.
Published Version
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