Extended Data Fig. 7: Refinement of the neutron diffraction dataset collected in the triple-q phase.

a, Comparison of observed and calculated intensities for the fractional antiferromagnetic skyrmion lattice. The dataset was collected in the triple-q phase under a magnetic field of 3.5 T along the [111] direction. b, Dependence of the R_F2 factor on the phase factor ϕ₁₁₁. The arrows indicate results for ϕ₁₁₁ = −π, −3π/2 and −9π/8, which correspond to the triple-q structures with helical, collinear and distorted helical components, respectively. The error bars correspond to the standard deviations of the measured neutron intensities (a) and the refined phase factor (b). c, Magnetic textures for one sublattice in the (111) plane with ϕ₁₁₁ = −9π/8, −π and −7π/8, showing that in the region −9π/8 ≤ ϕ₁₁₁ ≤ −7π/8 the triple-q structure always realizes a fractional antiferromagnetic skyrmion lattice, and only the proportion of fractionalization is varied. The colour scheme indicates the spin component along the [111] direction, and the arrows show the spin component in the (111) plane.