Skyrmion Lattice Domains in Fe1-xCoxSi

The strongly doped semiconductor Fe1-xCoxSi displays a dome of helimagnetic order for 0.05 ≤ x ≤ 0.7. We report small angle neutron scattering of the magnetic structure in the skyrmion lattice phase of Fe1-xCoxSi for x = 0.2 and magnetic field parallel to a crystallographic (100) direction. We observe twelve equally spaced maxima of scattering intensity on a ring, with an underlying six-fold symmetry of two sets of six spots. The intensity distribution suggests the formation of two degenerate skyrmion lattice domain populations with respect to the four-fold symmetry of the (100) directions in the scattering plane.