Spin-Wave Dispersion Relation for Holmium in the Spiral Magnetic Phase

Abstract

The spin‐wave dispersion relation for the c direction of holmium metal in its plane‐spiral magnetic phase has been studied by coherent inelastic scattering of thermal neutrons. Constant‐Q measurements of neutron energy loss processes, with the scattered neutron energy held fixed at 8.5 meV, were made at 78° and 48°K. Preliminary least‐squares analyses of the data indicate that the out‐of‐plane anisotropy constant is smaller than that for Dy and Tb, and that five interplanar exchange constants are required in order to fit the data satisfactorily. The resulting exchange constants are larger in magnitude than the anisotropy constant and are both positive and negative in sign as expected for the stability of the spiral structure.