Neutron Brillouin scattering with pulsed spallation neutron source - spin-wave excitations from ferromagnetic powder samples -

Neutron Brillouin scattering (NBS) method was developed using a pulsed spallation neutron source, and the feasibility of NBS was demonstrated by observing ferromagnetic spin waves in La${}_{0.8}$Sr${}_{0.2}$MnO${}_3$ and SrRuO${}_3$ powders. Gapless spin-wave excitations were observed in La${}_{0.8}$Sr${}_{0.2}$MnO${}_3$, which were continuously extended 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 SrRuO${}_3$ indicating robust spin-orbit coupling.