Ir from neutron spectroscopy measurements.*

Inelastic neutron scattering measurements of the fcc kagome antiferromagnet Mn₃Ir were performed using the SEQUOIA spectrometer at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). Comparison of the observed magnetic excitations to calculated spin waves, using exchange parameters derived from Density Functional Theory (DFT) calculations¹, confirms that 4 exchange parameters are needed to describe the spectra. However the values from DFT underestimate the bandwidth of the excitations. Using these values as initial parameters, fits to the model modified the 2 largest exchange parameters to match the bandwidth. A spin orbit correction to the the magnetic form factor was also provided by the fit. These results are consistent with effective spin orbit coupling mentioned in². Physically this means the magnetic moment is more extended than the free ion value.
¹ L. Szunyogh et al. Phys. Rev B. 79, 020403(R) (2009)
² H. Chen, Q. Niu, and A. H. MacDonald Phys. Rev. Lett. 112, 017205 (2014)