Spin-Wave Dispersion Relations in Gadolinium

Spin-wave dispersion relations have been measured in high-symmetry directions for metallic Gd. Analysis shows that at least five interplanar constants are required for a satisfactory fit to the data. The energy gap at $q=0\mathrm{}$ is unmeasurably small. In the $c$ direction the measured dispersion curve gives directly the Fourier-transformed exchange interaction $J\left(0\right)-J\left(q\right)\mathrm{}$. This exhibits no other extreme value except that at the origin.