Neutron-scattering study of the magnon energies and intensities in iron

The magnetic inelastic neutron scattering at low temperatures has been measured from a large single crystal of ${}_{}{}^{54}{}_{}{}^{}\mathrm{Fe}$(12 at.% Si) up to energy transfers of 100 meV using the constant-Q spectrometer at the Los Alamos pulsed neutron source. The spin-wave energies and intensities were obtained from the data by using a multichannel maximum-entropy technique, and we show that much more detailed information can be obtained from the maximum-entropy analysis. The observed spin-wave dispersion relations obtained in the present experiment are in excellent agreement with earlier data, and we observe a sharp falloff of the (001) magnon intensity at approximately 80 meV, which is in accord with previous experimental measurements and multiband theoretical calculations of the dynamic susceptibility of iron. We also compare the data rate obtained with the constant-Q spectrometer to a triple-axis instrument and find that the spectrometer is competitive for this type of measurement.