Polarized neutron study of alpha-RuCl3

The magnetic insulator alpha-RuCl3 features a layered honeycomb structure of edge-sharing octahedrally coordinated Ru3+ ions. The Ru ion is in the low-spin ground state and exhibits strong spin-orbit coupling making alpha-RuCl3 an interesting candidate for investigating physics related to the Kitaev model. Even though it orders magnetically at low temperatures, alpha-RuCl3 exhibits a spectrum of magnetic excitations which includes a continuum previously identified as a signature of fractionalized excitations characteristic of quantum spin liquids.
We have carried out polarized neutron scattering measurements enabled through the availability of large high-quality single crystals. Elastic scattering allows for a direct determination of the direction of the ordered spin moment while inelastic scattering confirms the magnetic nature and provides additional information about the character of the magnetic excitations seen above and below T_N. The results constrain the theoretical description of the effective spin Hamiltonian describing alpha-RuCl3.