Measuring Atomic Magnetic Moments in Magnetic Nanostructures Using X-Ray Magnetic Circular Dichroism (XMCD)

Abstract

The chapter describes the development of X-ray magnetic circular dichroism (XMCD) using circularly polarised soft X-ray photons from synchrotron sources. Following the derivation of X-ray absorption sum rules for magnetic materials, the technique became a powerful probe of magnetism able to separately measure the atomic and spin orbital magnetic moments independently for each magnetic element in the sample. The majority of the experiments have focused on the L-absorption edges of transition metals and the method has been particularly useful in identifying the source of enhanced magnetic moments in nanostructures. The chapter illustrates the power of the method with a specific example, that of Fe@Cr core–shell nanoparticles with different Cr shell thicknesses. Here, it was shown that at least two Cr atomic layers are required to see the onset of the exchange bias effect at the ferromagnetic–antiferromagnetic interface. The future perspectives of the technique are described including spatially resolved XMCD and time-resolved XMCD measurements.