We report on the measurements of the spin-wave stiffness A and its temperature dependence close to TC for two compounds: FeGe and the solid solution Fe0:8Mn0:2Ge. The small-angle neutron scattering was used to detect the inelastic scattering in the magnetic field above the transition from the conical to the eld-polarized state. This inelastic contribution is shaped as two circles on a
scattering map. Their radius is directly related to the spin wave stiffness A that decreases with a temperature but has a finite value at TC for both compounds. As for second-order phase transition it would be expected that the spin wave softens near Tc, this is not observe, which indicates the first order nature of the transition. that classifies the order-disorder phase transition in FeGe-based
compounds as the first order one.