Half-magnetization plateau and the origin of threefold symmetry breaking in an electrically switchable triangular antiferromagnet

We perform high-field magnetization measurements on the triangular lattice antiferromagnet Fe_{1/3}NbS_{2}. We observe a plateau in the magnetization centered at approximately half the saturation magnetization over a wide range of temperature and magnetic field. From density functional theory calculations, we determine a likely set of magnetic exchange constants. Incorporating these constants into a minimal Hamiltonian model of our material, we find that the plateau and the Z_{3} symmetry-breaking ground state both arise from the competition of interplane and intraplane exchange interactions. These findings are pertinent to the magnetoelectric properties of Fe_{1/3}NbS_{2}, which allow electrical switching of antiferromagnetic textures at relatively low current densities.