Two methods to study inelastic neutron-scattering measurements based on ω n (q) versus S(q, ω) applied to the magnetic open honeycomb lattice Tb2Ir3Ga9

This work describes two methods to fit the inelastic neutron-scattering spectrumS(q,ω) with wavevectorqand frequencyω. The common and well-established method extracts the experimental spin-wave branchesωn(q) from the measured spectraS(q,ω) and then minimizes the difference between the observed and predicted frequencies. Whennbranches of frequencies are predicted but the measured frequencies overlap to produce onlym < nbranches, 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 intensitiesS(q,ω) over a grid {qi,ωj} 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 Tb2Ir3Ga9.