Magnetic excitations in the itinerant antiferromagnetsMn3Si and Fe-dopedMn3Si

Magnetic excitations in the itinerant antiferromagnets ${\mathrm{Mn}}_3$Si and Fe-doped ${\mathrm{Mn}}_3$Si have been measured at low temperatures by inelastic scattering of neutrons. ${\mathrm{Mn}}_3$Si is an incommensurate antiferromagnetic with magnetic Bragg points of the form (h,k,l)±(δ,δ,δ) with δ=0.425. Fe-doped ${\mathrm{Mn}}_3$Si is a commensurate antiferromagnet with δ=(1/2. Its low-energy magnetic excitations have a linear dispersion relation with a slope of approximately 30 meV Å, but above 6 meV, the slope increases so that the ‘‘cone’’ of the dispersion relation becomes a ‘‘chimney.’’ Well-defined excitations have been observed at energies up to 7.5$k_B$ $T_N$ (15 meV). In pure ${\mathrm{Mn}}_3$Si, a similar dispersion cone exists around each satellite magnetic Bragg point with a slope of approximately 37 meV Å. The two dispersion cones from a pair of satellite points intersect at about 5 meV. Above this energy the intensity of the inelastic peaks changes drastically, indicating a strong interaction between the cones. For both phases, the damping is very large and increases almost linearly with energy.