Two methods to study inelastic neutron-scattering measurements based on ω n ( q ) versus S ( q , ω ) applied to the magnetic open honeycomb lattice Tb 2 Ir 3 Ga 9 .

This work describes two methods to fit the inelastic neutron-scattering spectrum S ( q , ω ) with wavevector q and frequency ω . The common and well-established method extracts the experimental spin-wave branches ω n ( q ) from the measured spectra S ( q , ω ) and then minimizes the difference between the observed and predicted frequencies. When n branches of frequencies are predicted but the measured frequencies overlap to produce only m < n branches, the weighted average of the predicted frequencies must be compared to the observed frequencies. A penalty is then exacted when the width of the predicted frequencies exceeds the width of the observed frequencies. The second method directly compares the measured and predicted intensities S ( q , ω ) over a grid { q i , ω j } in wavevector and frequency space. After subtracting background noise from the observed intensities, the theoretical intensities are scaled by a simple wavevector-dependent function that reflects the instrumental resolution. The advantages and disadvantages of each approach are demonstrated by studying the open honeycomb material Tb 2 Ir 3 Ga 9 .