Neutron Brillouin Scattering with Pulsed Spallation Neutron Source --- Spin-Wave Excitations from Ferromagnetic Powder Samples ---

The neutron Brillouin scattering (NBS) method, which was developed using advanced neutron sources, was extended to an intense pulsed spallation neutron source. The feasibility of this method was demonstrated by observing ferromagnetic spin waves in La0.8Sr0.2MnO3and SrRuO3powders. Gapless spin-wave excitations were observed in La0.8Sr0.2MnO3, which were continuously extrapolated to the lower scattering vector $Q$ from previous results using single crystals. The novel result is a well-defined quadratic $Q$ dependence in the spin-wave dispersion curve with a large energy gap in SrRuO3.