Kerrrotation

Kerr rotation refers to the rotation of the plane of polarization of linearly polarized light upon reflection from a magnetized material, a key part of the magneto-optical Kerr effect (MOKE). The rotation angle, known as the Kerr rotation, may be accompanied by a change in ellipticity as the polarization state becomes slightly elliptical after reflection.

The effect arises from magnetization-induced off-diagonal components of the optical dielectric tensor. These components couple the electric field components of the incident light, producing different complex reflectivities for the electric field components and resulting in a rotated and possibly elliptically polarized reflected beam. The Kerr rotation depends on the material’s magnetization, the wavelength of light, the incidence angle, and the optical constants of the surface.

There are three common geometries, corresponding to the orientation of the magnetization relative to the sample surface and the plane of incidence: polar Kerr, longitudinal Kerr, and transverse Kerr. In polar Kerr geometry the magnetization is perpendicular to the surface; in longitudinal Kerr it lies in the surface plane and parallel to the plane of incidence; in transverse Kerr it lies in the surface plane but perpendicular to the plane of incidence. Each geometry produces characteristic rotation signals used to probe magnetic properties.

Historically, the effect was observed by John Kerr in 1877. Today Kerr rotation is widely used to characterize magnetic thin films and domains, study ultrafast magnetization dynamics with pump–probe techniques, and read magnetic information in magneto-optical storage technologies. It is related to, but distinct from, the Faraday rotation observed in transmitted light.