Magnetic excitations in Fe-doped Mn3Si

Abstract

Inelastic scattering of neutrons has been used to study the magnetic excitations in Fe-doped Mn3Si at 7 K. Mn3Si is an incommensurate antiferromagnet with magnetic Bragg points of the form (h,k,l)±(δ,δ,δ) with δ=0.425. Its magnetic excitations are qualitatively similar to those of the γ-Mn alloys, or of the itinerant antiferromagnet, chromium. The addition of 5 at. % of iron causes the value of δ to change to 1/2, so that the material becomes a commensurate antiferromagnet, greatly simplifying the shape of the excitation spectrum. In addition the low Néel temperature (23 K) permits measurements to be extended to energies of several times kTN. Constant energy scans through a magnetic Bragg point are qualitatively consistent with the spin-wave dispersion relation forming a ‘‘cone’’ around the magnetic Bragg point. Low-energy scans (1 meV≤ΔE≤4 meV) are centered on the Bragg point and flat-topped, while at higher energies (5 meV≤ΔE≤15 meV) the peak is clearly resolved as double. A fit using a damped-harmonic oscillator cross section suggests that the slope of the dispersion relation increases with energy, and that the excitations are highly damped.