Magneto-optic Kerr effect

In contrast, the magneto-optic Kerr effect describes changes to light reflected from a magnetic surface.

Both effects result from the off-diagonal components of the dielectric tensor

is the magnetic permeability; and thus the speed of light varies depending on its orientation.

is the angle that linearly polarized light will be rotated after hitting the sample.

(not to be confused with ellipticity from mathematics) is the ratio of the semimajor and semiminor axes of the elliptically polarized light, generated from reflection of linearly polarized light.

[1] MOKE can be further categorized by the direction of the magnetization vector with respect to the reflecting surface and the plane of incidence.

In the longitudinal effect, the magnetization vector is parallel to both the reflection surface and the plane of incidence.

vectors, namely the standard Fresnel amplitude coefficient of reflection

When the magnetization is perpendicular to the plane of incidence and parallel to the surface it is said to be in the transverse configuration.

This change in reflectivity is proportional to the component of magnetization that is perpendicular to the plane of incidence and parallel to the surface, as above.

If the magnetization component points to the right of the incident plane, as viewed from the source, then the Kerr vector adds to the Fresnel amplitude vector and the intensity of the reflected light is

On the other hand, if the component of magnetization component points to the left of the incident plane as viewed from the source, the Kerr vector subtracts from the Fresnel amplitude and the reflected intensity is given by

In addition to the polar, longitudinal and transverse Kerr effect which depend linearly on the respective magnetization components, there are also higher order quadratic effects,[2] for which the Kerr angle depends on product terms involving the polar, longitudinal and transverse magnetization components.

Quadratic magneto-optic Kerr effect (QMOKE) is found strong in Heusler alloys such as Co2FeSi and Co2MnGe[3][4] A Kerr microscope relies on the MOKE in order to image differences in the magnetization on a surface of magnetic material.

In a Kerr microscope, the illuminating light is first passed through a polarizer filter, then reflects from the sample and passes through an analyzer polarizing filter, before going through a regular optical microscope.

A computer system is often used to create an image of the magnetic field on the surface from these changes in polarization.

The laser would heat the platter above its Curie temperature at which point the electromagnet would orient that bit as a 1 or 0.

To read, the laser is operated at a lower intensity, and emits polarized light.

Reflected light is analyzed showing a noticeable difference between a 0 or 1.