Magnetic Excitations in Uranium Dioxide

Abstract

The spin-wave dispersion relations have been measured in antiferromagnetic uranium dioxide by inelastic neutron-scattering techniques. The triple-axis crystal spectrometer at the C5 facility of NRU was used throughout in its constant-Q mode of operation. The dispersion relations were obtained for spin waves propagating along the main symmetry directions at 9\ifmmode^\circ\else\textdegree\fi{}K, and less complete measurements were made at higher temperatures both above and below the N\'eel temperature. The theory of spin waves in U${\mathrm{O}}_{2}$ is developed and various models are used in attempts to deduce the exchange and anisotropy parameters from the experimental results. None of the models are completely satisfactory, because of the difficulties arising from the multidomain character of the specimen, and from the strong interaction between the magnons and the phonons. A theory of this interaction is also developed which gives quite reasonable agreement with experiment.