Strongly two-dimensional exchange interactions in the in-plane metallic antiferromagnet Fe$_2$As probed by inelastic neutron scattering

TL;DR

This study investigates the magnetic interactions in Fe$_2$As using inelastic neutron scattering and theoretical modeling, revealing strongly two-dimensional exchange interactions despite the material's three-dimensional structure.

Contribution

The paper provides new experimental data and refined exchange coupling constants for Fe$_2$As, highlighting unexpectedly strong in-plane interactions in a metallic antiferromagnet.

Findings

Strong in-plane Fe-Fe exchange interactions identified

Experimental magnon spectra broadly match theoretical predictions

Difficulty in determining full exchange interactions due to energy limitations

Abstract

To understand spin interactions in materials of the Cu$_2$Sb structure type, inelastic neutron scattering of Fe$_2$As single crystals was examined at different temperatures and incident neutron energies. The experimental phonon spectra match well with the simulated phonon spectra obtained from density functional theory (DFT) calculations. The measured magnon spectra were compared to the simulated magnon spectra obtained via linear spin wave theory with the exchange coupling constants calculated using the spin polarized, relativistic Korringa-Kohn-Rostoker method in Zhang et al. (2013). The simulated magnon spectra broadly agree with the experimental data although, the energy values are underestimated along the $K$ direction. Exchange coupling constants between Fe atoms were refined by fits to the experimental magnon spectra, revealing stronger nearest neighbor Fe1-Fe1 exchange coupling than previously reported. The strength of this exchange coupling is almost an order of magnitude higher than other exchange interactions despite the three-dimensional nature of the phonon interactions. The lack of scattering intensity at energies above 60 meV makes unconstrained determination of the full set of exchange interactions difficult, which may be a fundamental challenge in metallic antiferromagnets.