Spin Waves in Manganese Monoxide

The spin waves in MnO have been studied at various temperatures from 4.2 K to the Néel temperature T_N of 117 K by means of neutron inelastic scattering techniques. The dispersion curves in the [001], [111] and [111] direction have been determined. Using the spin Hamiltonian with distance dependent n.n. interaction, n.n.n. interaction and dipole-dipole interaction, the spin wave theory involving magnon-magnon interaction has been developed. It has been found that the theory interprets not only the spin wave dispersion curves at 4.2 K but also its temperature dependence up to T⁄T_N=0.9. The magnon density of states has been calculated.