Multiple-q noncollinear magnetism in an itinerant hexagonal magnet

Multiple- q spin order, i.e., a spin texture characterized by a multiple number of coexisting magnetic modulation vectors q , has recently attracted attention as a source of nontrivial magnetic topology and associated emergent phenomena. One typical example is the triple- q skyrmion lattice state stabilized by Dzyaloshinskii-Moriya interactions in noncentrosymmetric magnets, while the emergence of various multiple- q states of different origins is expected according to the latest theories. Here, we investigated the magnetic structure of the itinerant polar hexagonal magnet Y 3 Co 8 Sn 4 , in which several distinctive mechanisms favoring multiple- q states are allowed to become active. Small-angle neutron-scattering experiments suggest the formation of incommensurate triple- q magnetic order with an in-plane vortex-like spin texture, which can be most consistently explained in terms of the novel four-spin interaction mechanism inherent to itinerant magnets. The present results suggest a new route to realizing exotic multiple- q orders and that itinerant hexagonal magnets, including the R 3 M 8 Sn 4 family with wide chemical tunability, can be a unique material platform to explore their rich phase diagrams.