Neutron scattering investigations of muItiferroic 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 TN ≅ 70 K and have shown the existence of persistent albeit heavily damped spin waves. (author)