The "inclined" dynamics method developed for studying spin waves in ferromagnets was proposed and implemented at the Leningrad Nuclear Physics Institute in Gatchina in the mid-1980s. The method is based on the analysis of the left-right asymmetry in magnetic scattering of polarized neutrons, which occurs when the magnetization direction in a sample is inclined with respect to the wave vector of the incident beam. Neutron scattering by spin waves is concentrated inside a cone bounded by a critical (cutoff) angle equal to the magnon-to-neutron mass ratio. By measuring this ratio, the magnon mass and the spin wave stiffness in a ferromagnetic material are found. The experiments on measuring the spin wave stiffness in helimagnets with the Dzyaloshinskii-Moriya interaction by the method of small-angle polarized neutron scattering show the validity of quadratic dispersion law shifted in the field direction by the value of the spiral wave vector:is an element of(q) = A(q - k)(2) - g mu(B)(H - H-C2). The spin wave stiffness has been measured as a function of temperature for binary and quasi-binary compounds: MnSi, Mn(1-x)FexSi, FeGe, Mn1-xFexGe,Fe1-xCoxSi, Cu2OSeO3.
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