Helimagnetism
Helimagnetism is an incommensurate form of magnetic ordering that results from the competition between ferromagnetic and antiferromagnetic exchange interactions, and is typically only observed at liquid helium temperatures. Spins of neighbouring magnetic moments arrange themselves in a spiral or helical pattern, with a characteristic turn angle of somewhere between 0 and 180 degrees. It is possible to view ferromagnetism and antiferromagnetism as helimagnetic structures with characteristic turn angles of 0 and 180 degrees respectively. Helimagnetic order breaks spatial inversion symmetry, as it can be either left-handed or right-handed in nature.
Helimagnetism was first proposed in 1959, as an explanation of the magnetic structure of manganese dioxide. Initially applied to neutron diffraction, it has since been observed more directly by Lorentz electron microscopy. Some helimagnetic structures are reported to be stable up to room temperature.
