Toroidal ordering in crystals

Phase transitions to ordered states, which correspond to the toroidal family of multipoles known in electrodynamics, are discussed. The ordering of toroidal moments may either occur simultaneously with their formation (as in superconductivity) or may follow it (at lower temperatures). In addition to electrodynamic toroidal moments corresponding to either poloidal charge currents or a spin configuration, a toroidal state corresponding to poloidal spin currents is possible.