Probing surface and thin film magnetic structure with circularly polarized synchrotron radiation

Abstract

A new group of techniques predicated on the availability of a tunable source of circularly polarized soft x-rays show tremendous potential for advancing the understanding of magnetic nanostructures. These techniques involve use of circularly polarized radiation as probes in x-ray absorption and x-ray photoemission and photoelectron diffraction studies, and provide unique information about the element specific magnetic moments and magnetic structure of thin films, interfaces, and surfaces. Examples of each technique will be discussed with emphasis given to the recently demonstrated first observation of spin-dependent photoelectron diffraction using circularly polarized x-rays. This technique promises the direct, element specific determination of local magnetic structure on an atomic scale, and will be of tremendous utility in the effort to establish structure-property relationships in magnetic nanostructures. Circularly polarized x-rays are used to produce spin-polarized photoelectrons from the Fe 2p spin-orbit doublet. Intensity asymmetries of up to ∼3% are observed for the 2p3/2 sublevel. These asymmetries depend on the relative orientation of the x-ray polarization vector and the sample magnetization as well as upon the photoelectron kinetic energy and emission direction. Multiple scattering calculations are found to reproduce both the observed energy and angular asymmetry variations. Strategies to increase the measured effect are also discussed.