Noncollinear kagome magnet driven by giant antisymmetric exchange

Kagome lattices host exotic phenomena such as quantum spin liquids, topological Weyl nodes, and flat bands. The kagome ferromagnet Co3Sn2S2 has been a focus of debate due to conflicting reports on its magnetic character. Here, using weakly perturbative probes—primarily neutron scattering and Mössbauer spectroscopy—we determine its ground state and magnetic Hamiltonian. The spin wave spectrum is reproduced by a simple Hamiltonian dominated by a large in-plane nearest-neighbor Heisenberg interaction J and an antisymmetric Dzyaloshinskii-Moriya interaction that is roughly one third of J. This Hamiltonian yields a canted, noncollinear ferromagnetic ground state with an umbrella-type structure, which our data show to be the true ground state at all temperatures below TC. Additionally, the spin susceptibility above TC exhibits a reduced critical exponent, akin to other spin-anisotropic systems. Our findings explain the unconventional magnetism in Co3Sn2S2, including the giant anomalous Hall effect and the origin of chiral phonons. The magnetic ground state of the kagome magnet Co3Sn2S2 has been the subject of numerous recent studies. Here, the authors study the ground state and magnetic Hamiltonian of Co3Sn2S2 and provide results consistent with a canted umbrella structure and a large Dzyaloshinskii-Moriya interaction term.