Spin-Wave Dispersion Relation in Dysprosium Metal

Abstract

The spin-wave dispersion relation for the $c$ direction of dysprosium metal in the ferro-magnetic phase at 78°K and in the helical magnetic phase at 98°K has been measured by triple-axis neutron spectrometry. The energy gap measured in the ferromagnetic phase at $\overrightarrow{\mathrm{q}}=0\mathrm{}$ is in poor agreement with that calculated from the macroscopic magnetostriction and crystal-field anisotropy constants. The Fourier-transformed exchange interaction $J\left(\overrightarrow{\mathrm{q}}\right)-J\left(0\right)\mathrm{}$ in the ferromagnetic phase posses a peak near the wave vector that gives the periodicity of the helical structure just above the Curie temperature.