X-Ray Magnetic Circular Dichroism: Basic Concepts and Theory for 3D Transition Metal Atoms

TLDR: In this article, the basic theory underlying the x-ray magnetic circular dichroism technique with emphasis on 3D transition-metal atoms is discussed from an elementary level and illustrated by model calculations using an atomic picture and a simple Hamiltonian that accounts for the spin-orbit and exchange interactions.

Abstract: We discuss the basic theory underlying the x-ray magnetic circular dichroism technique with emphasis on 3d transition-metal atoms. The basic concepts are developed from an elementary level and illustrated by model calculations using an atomic picture and a simple Hamiltonian that accounts for two key interactions associated with the dichroism effect: the spin-orbit and exchange interactions. We present calculations for a one-electron model that is shown to be equivalent to a configuration-based model for the d 9 configuration and discuss the relationship between the measured dichroism signal and the spin, orbital, and total magnetic moments. Our results can be cast into a simple two-step model that considers the core shell as the “source” of photoelectrons with polarized spin and/or angular momentum and the valence shell as a spin- or angular-momentum resolving “detector.” We also point out that, according to the initial-state rule, the dichroism intensity is linked to the ground-state d-shell occupancy and moments.