Persistent spin waves above the Neel temperature in YMnO3

We have investigated the spin excitations in the frustrated triangular antiferromagnet YMnO3 by inelastic neutron scattering in the ordered magnetic state and also above the Neel temperature. In the ordered phase, we observe broad spin excitations, which can be described by an anisotropic Heisenberg model. Above T-N, well defined signatures of persistent spin waves were found evidenced by inelastic peaks in energy spectra. Neatly separated excitations from the quasielastic fluctuations have been identified in this two-dimensional magnetic system. The clear observation might be related to the geometrical frustrated and short ranged ordered nature of this triangular antiferromagnet.