A 1ST-PRINCIPLES THEORY OF X-RAY FARADAY EFFECTS

We present a first-principles theory of x-ray Faraday effects. Initially we calculate the difference in absorption rate for right and left circularly polarized incident radiation. From this we are able to define an effective dielectric tensor that can be used to calculate magneto-x-ray properties. This work is based on a fully relativistic scattering-theory description of the electronic structure of magnetic materials. The theory is illustrated by a calculation of the Faraday rotation and induced ellipticity in linearly polarized light incident at the K edge of iron. Recent experiments compare favourably with the theory.