Impact of further-range exchange and cubic anisotropy on magnetic excitations in the fcc kagome antiferromagnet IrMn3

TL;DR

This study models magnetic excitations in IrMn3 using a classical Heisenberg approach, highlighting the importance of further-range exchange interactions and cubic anisotropy for accurately matching neutron scattering data.

Contribution

It introduces the inclusion of up to fourth nearest neighbor exchange interactions and cubic anisotropy in modeling IrMn3's magnetic excitations, extending previous theoretical work.

Findings

Further-range exchange interactions are essential for data agreement.

Energy gap estimates support strong cubic anisotropy.

Model aligns well with experimental neutron scattering results.

Abstract

Exchange interactions up to fourth nearest neighbor are shown within a classical local-moment Heisenberg approach to be important to model inelastic neutron scattering data on the fcc kagome antiferromagnet IrMn$_3$. Spin wave frequencies are calculated using the torque equation and the magnetic scattering function, $S({\bf Q},\omega)$, is determined by a Green's function method, as an extension of our previous work, LeBlanc et al, Phys. Rev. B 90, 144403 (2014). Results are compared with intensity contour data on powder samples of ordered IrMn$_3$, where magnetic Mn ions occupy lattice sites of ABC stacked kagome planes. Values of exchange parameters taken from DFT calculations used in our model provide good agreement with the experimental results only if further-neighbor exchange is included. Estimates of the observed energy gap support the existence of strong cubic anisotropy predicted by DFT calculations.