Neutron scattering investigations of multiferroic YMnO3

Multiferroic materials are the materials that show several cooperative ordering phenomena simultaneously. Here we consider only those materials that show both antiferromagnetism and ferroelectricity and in which the ordering parameters are coupled to each other. I shall review our recent neutron scattering investigations on multiferroic hexagonal manganites YMnO₃. We have determined the spin wave dispersions in YMnO₃ in symmetry directions by inelastic neutron scattering and have fitted the results with a simple nearest-neighbour anisotropic Heisenberg model. We have investigated the spin dynamics of YMnO₃ above T _N ∼ 70 K and have shown the existence of persistent albeit heavily damped spin waves.