Damped spin-wave excitations in the itinerant antiferromagnet $\gamma$-Fe$_{0.7}$Mn$_{0.3}$

TL;DR

This study investigates spin-wave excitations in the antiferromagnetic $ ext{γ}$-Fe$_{0.7}$Mn$_{0.3}$ using inelastic neutron scattering, revealing damping and dispersion deviations at high energies, indicating interaction with particle-hole excitations.

Contribution

First detailed analysis of high-energy spin-wave damping and dispersion in $ ext{γ}$-Fe$_{0.7}$Mn$_{0.3}$ using neutron scattering, highlighting unique damping behavior.

Findings

Spin excitations remain isotropic up to 78 meV.

Damping parameter reaches 110 meV at 78 meV energy.

Spin-wave dispersion deviates above 40 meV, merging with particle-hole continuum.

Abstract

The collective spin-wave excitations in the antiferromagnetic state of $\gamma$-Fe$_{0.7}$Mn$_{0.3}$ were investigated using the inelastic neutron scattering technique. The spin excitations remain isotropic up to the high excitation energy, ${\hbar\omega}= 78$ meV. The excitations gradually become broad and damped above 40 meV. The damping parameter ${\gamma}$ reaches 110(16) meV at ${\hbar\omega} = 78$ meV, which is much larger than that for other metallic compounds, e.g., CaFe$_2$As$_2$ (24 meV), La$_{2-2x}$Sr$_{1+2x}$Mn$_2$O$_7$ ($52-72$ meV), and Mn$_{90}$Cu$_{10}$ (88 meV). In addition, the spin-wave dispersion shows a deviation from the relation $({\hbar\omega})^2 = c^2q^2 + {\Delta}^2$ above 40 meV. The group velocity above this energy increases to 470(40) meV{\AA}, which is higher than that at the low energies, $c = 226(5)$ meV{\AA}. These results could suggest that the spin-wave excitations merge with the continuum of the individual particle-hole excitations at 40 meV.