Direct evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV4S8

We report small-angle neutron scattering studies of the lacunar spinelGaV(4)S(8), which reveal the long-wavelength magnetic phases to be cycloidally modulated. Upon cooling, these modulated phases, including a recently proposed Neel-type skyrmion phase, transform into a simple ferromagnetic state. These results indicate the modulated phases in GaV4S8 gain their stability from thermal fluctuations, while at lower temperatures the ferromagnetic state emerges in accord with the strong easy-axis magnetic anisotropy. Crucially, our study provides microscopic evidence that the skyrmions in GaV4S8 indeed display a Neel-type helicity. More generally, our approach can be applied to evidence the helicity of any bulk skyrmion phase.