We study the helimagnetic ground state of the MnGe cubic alloy using small-angle neutron scattering and a high-resolution method, the so-called MIEZE spectroscopy. Upon cooling below the Néel temperature$T_{\mathrm{N}}=170\left(5\right)\mathrm{K}$, we observe the proliferation of long-wavelengthgapless spin fluctuations, concomitant with a continuous evolution of the helical correlation length. These fluctuations disappear at$T_{\mathrm{com}}=32\left(5\right)\mathrm{K}$ when the helical period becomes commensurate with the lattice. We propose to describe this intermediate phase as a soliton lattice, promoting nonlinear collective modes, orphasons, over a large temperature interval. We discuss the possible relevance of our results to the previously observed magnetotransport anomalies.

• Magnetic phase transitions
• Magnetization dynamics
• Chiral magnets
• Metals
• Noncollinear magnets
• Neutron scattering
• Neutron spin echo spectroscopy