X-ray magnetic circular dichroism-a high energy probe of magnetic properties

X-ray magnetic circular dichroism (XMCD) spectroscopy is a powerful emerging technique that measures difference in absorption of left- and right-circularly polarized X-rays by a magnetized sample, often at cryogenic temperatures. It is already well established in magnetic materials science, and it is likely to become a significant tool for the inorganic and bioinorganic communities. As with all X-ray spectroscopies, XMCD has the advantage of being element specific. Interpretation of the spectra can: provide quantitative information about the distribution of spin and orbital angular momenta from simple “sum rules”; determine spin orientations from the sign of the XMCD signal; infer spin states from magnetization curves; and separate magnetic and non-magnetic components in heterogeneous samples. With new synchrotron radiation sources and improved end stations, XMCD measurements on dilute samples such as metals in enzymes, are becoming more routine. This review first details the technology currently available for XMCD measurements and outlines the theory underlying interpretation of the spectra. It then illustrates the strengths of the XMCD technique using examples taken from bioinorganic chemistry and materials science. In this way, we aim to encourage chemists, materials scientists, and biologists to consider XMCD spectroscopy as an approach to understanding the electronic and magnetic structure of their samples.