Spin-wave dynamics in the helimagnet FeGe studied by small-angle neutron scattering

We have studied the spin-wave stiffness of the Dzyaloshinskii-Moriya helimagnet FeGe in a temperature range from 225 K up to T-C approximate to 278.7 K by small-angle neutron scattering. The method we have used is based on [Grigoriev et al., Phys. Rev. B 92, 220415(R) (2015)] and was extended here for the application in polycrystalline samples. We confirm the validity of the anisotropic spin-wave dispersion for FeGe caused by the Dzyaloshinskii-Moriya interaction. We have shown that the spin-wave stiffness A for the FeGe helimagnet decreases with a temperature as A(T) = 194[1 - 0.7(T/TC) 4.2] meV angstrom(2). The finite value of the spin-wave stiffness A = 58 meV angstrom(2) at TC classifies the order-disorder phase transition in FeGe as being the first-order one