A property possessed by some metals, alloys, and salts of transition elements in which the atomic magnetic moments, at sufficiently low temperatures, form an ordered array which alternates or spirals so as to give no net total moment in zero applied magnetic field. Figure 1 shows the simple antiparallel arrangement of manganese moments at temperatures below 72 K in the unit cell of manganese fluoride (MnF₂). The most direct way of detecting such arrangements is by means of neutron diffraction.