Spin waves in MnO; from 4°K to temperatures close to TN

Spin waves have been measured in MnO by inelastic scattering of neutrons from 4 °K to a temperature 0·25 °K below T_N. The 4 °K spectrum is interpreted in the frame of linear spin wave theory with effective exchange integrals J₁^? = 0·321 meV, J₁⁺ = 0·424 meV, J₂¹ = 0·446 meV and a phenomenological parameter for anisotropy D₁ = 0·059 meV. The effect of the actual dipole-dipole Hamiltonian is shown to give a priori a very good account of the lifting of the degeneracy of spin waves near the Brillouin zone center. The Bloch model for interacting spin waves and theories based on Green function approximations have been adapted to the MnO case, in order to compute the main properties (mean magnetization of a sublattice, anisotropic deformation, extra isotropic contraction and magnon spectrum) at many temperatures. Comparison of these with experimental results tends to favour a generalized Callen renormalization model, which gives an overall fit from 4 °K, to temperalures close to T_N.