Abstract The space group P6̄2 m has four different magnetic single modes: one ferro- and one antiferromagnetic mode ( S = Sc) and two types of triangular antiferromagnetic spin configurations. Coexistence of a ferromagnetic mode and a triangular mode is not possible for symmetry reasons. If, however, the C 2 v symmetry of the crystalline field potential decreases to σ v , or lower, a mixing can be energetically favorable. This means that the metamagnetic behavior of e.g. non-stoichiometric Fe 2P can be described in terms of a symmetry breaking perturbation. Expressions for the exchange energies of the different modes in a localized spin model, including anisotropy, are presented.