Spin-Wave Dispersion Relation for Er Metal at 4.5° K

Abstract

The spin-wave dispersion relation $\hslash \omega \left(\overrightarrow{\mathrm{q}}\right)$ for the $c$ direction of erbium metal in its conical magnetic phase has been studied by coherent inelastic scattering of thermal neutrons. The improved resolution of the present experiment compared with that used in earlier work on Er has permitted the first observation of both the distinct spin-wave branches corresponding to $\hslash \omega (+\overrightarrow{\mathrm{q}})$ and $\hslash \omega (-\overrightarrow{\mathrm{q}})$ over a wide range of $\left|\overrightarrow{\mathrm{q}}\right|$ As a consequence these results are the first to indicate that the anisotropic exchange interaction is a dominant interaction for a rare-earth metal and/or the model magnetic Hamiltonian generally employed for these metals is seriously inadequate.