Low temperature magnetic structure of the quasi 1-dimensional magnet Ni₂Si₄

Ni2Si₄, Liebenbergite, is an example of a quasi-one-dimensional magnet made up of frustrated corner sharing triangles of Ni²⁺ (S = 1) ions that propagate parallel to the b axis. Ni2Si₄ is isostructural with olivine, a common mineral of varying composition Fe_2-xMgxSi ₄, and is described in the orthorhombic space group Pnma. A synthetic polycrystalline sample of Ni2Si₄ was studied using powder neutron diffraction with spectra taken above and below the antiferromagnetic ordering transition (TN = 34 K). Analysis of the magnetic structure was carried out using the symmetry models of corepresentation theory. The refined spin structure evidences both ferromagnetic and antiferromagnetic inter-chain interactions, and ferromagnetic intra-chain coupling. The competition between the magnetic interactions can be seen in the canting of the moments away from a collinear arrangement.