A
magneto-optic effect is any one of a number of phenomena in which an
electromagnetic wave propagates through a medium that has been altered by the presence of a quasistatic
magnetic field. In such a material, which is also called
gyrotropic or
gyromagnetic, left- and right-rotating elliptical polarizations can propagate at different speeds, leading to a number of important phenomena. When light is transmitted through a layer of magneto-optic material, the result is called the
Faraday effect: the plane of
polarization can be rotated, forming a
Faraday rotator. The results of reflection from a magneto-optic material are known as the
magneto-optic Kerr effect (not to be confused with the
nonlinear Kerr effect).