Quadratic magnetic rotation (also known as QMR or QMR effect) is a type of magneto-optic effect, discovered in the mid 1980s by a team of Ukrainian physicists.
In contrast to the Faraday effect, QMR originates from the quadratic proportionality between the angle of the rotation of the plane of polarization and the strength of the magnetic field.
Mostly QMR can be observed in the transverse geometry when the vector of the magnetic field strength is perpendicular to the direction of light propagation.
The first evidence of QMR effect was obtained in the antiferromagnetic crystal of cobalt fluoride in 1985.
Onsager's reciprocal relations generalized for magnetically ordered media eliminate symmetry restrictions for QMR in the media which have lost the center of anti-inversion as an operation of symmetry at an ordering of its magnetic subsystem.