Circular dichroism in 4f photoemission from magnetically ordered rare-earth materials

4f Photoemission (PE) spectra from magnetically ordered rare-earth materials using circularly polarized X-rays exhibit strong Magnetic Circular Dichroism (MCD), i.e., the intensities of the individual multiplet lines depend on the relative orientation of sample magnetization and photon spin. On the example of the wellresolved Tb 4f PE multiplet, it is shown that in relevant cases 4f PE lines are essentially only observed for one magnetization direction, either parallel or antiparallel to the photon spin. These large MCD effects in 4f PE open new perspectives in the analysis of surface and thin-film magnetism and provide a sensor for the degree of circular polarization of soft X-rays over a wide photon-energy range. To demonstrate the potential of MCD in 4f PE as a magnetometer, we studied Gd(0001) and Tb(0001), where the magnetization of the topmost atomic (0001) layer can be easily separated from the bulk magnetization via the surface core-level shift. In multicomponent magnetic thin films containing different rare-earth elements 4f PE allows to monitor magnetization in an element-specilic way, e.g., in case of the hetero-magnetic interface 1 ML En/Gd(0001).