A1. Fundamentals of magneto-optics.
In 1845 Michael Faraday discovered that the polarization of light propagating through a magnetized substance is rotated. This magneto-optical effect, first observed in a sample of glass placed in an intense magnetic field and later in the reflectivity of metals by John Kerr, is now a widely used physical method to explore the properties of magnetic materials. The magneto-optical Kerr and Faraday effects are due to an asymmetric absorption and refraction for the left and right helicities of circularly polarized light due to the spin-orbit interaction. In the linear response theory these effects are well described by the off-diagonal complex dielectric tensor element εxy. For example, the Kerr rotation θK and ellipticity ηK acquired by a linearly polarized light reflected from a ferromagnet is given, in the polar geometry, by :