Toroidal Magnetism in the Chiral-Triangular-Lattice Material BaCoSiO₄ studied with Diffuse Neutron Scattering.

BaCoSiO₄ has a hexagonal crystal structure in which distortions lead to a trimerization of the magnetic Co ions as well as inducing a chirality in the unit cell. In zero-field, the material undergoes a magnetic transition to a Ferritoroidal ground state where spins in a trimer are arranged ``head-to-tail'' to form a magnetic toroid. The five nearest neighbour interactions, as well as the antisymmetric DM interaction, are all important in this material, leading to a complicated competition between interactions on this frustrated lattice. The ground state structure, however, can be simply explained by three interpenetrating toroidal sublattices, one of which has a torroidal moment opposite to the other two. Extensive diffuse structural scattering indicates the presence of short-range correlations within the crystal structure, while diffuse magnetic scattering near the transition indicates the material is magnetically frustrated. The origin of the diffuse structural scattering is still under investigation; however, strong high Q scattering indicates local displacements are likely the cause. Using the magnetic diffuse scattering data, we aim to validate the magnetic Hamiltonian previously used to describe the magnetic diffraction data.