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arXiv · 1612.02515

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

S. Ibuka·S. Itoh·T. Yokoo·Y. Endoh
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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.

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S. Ibuka, S. Itoh, T. Yokoo, Y. Endoh. 2016-12-08. Damped spin-wave excitations in the itinerant antiferromagnet $\gamma$-Fe$_{0.7}$Mn$_{0.3}$. https://doi.org/10.1103/physrevb.95.224406

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