Interfaces of Ce/Fe and La/Fe multilayers probed by magnetic circular x-ray dichroism

An experimental study of conventional x-ray absorption and of magnetic circular x-ray dichroism has been performed on La/Fe and on Ce/Fe multilayers at the L2 and L3 edges of La and Ce and at the K edge of Fe to characterize the impact of the interaction of La or Ce and Fe on the local electronic and magnetic structure of the interfaces. The spectra reveal that the interaction is particularly unusual for Ce/Fe, where two effects have been observed. First, on a depth scale of at least 15 near the interface, the Ce atoms adopt the electronic structure of the α phase, with itinerant 4f states. Second, these α-phase-like Ce atoms are magnetically polarized and carry an ordered magnetic 5d spin moment. This moment is antiferromagnetically coupled to the Fe 3d moment. Interface mixing on a length scale of the magnetic polarization can be excluded. For the La/Fe system, a similar magnetic polarization is effective, but in contrast to Ce/Fe it is restricted to the immediate interface with Fe. The results are discussed with reference to recent measurements of the macroscopic magnetization and Mössbauer spectra. Comparison with intermetallic compounds of rare-earth and late transition-metal elements points to the importance of hybridization effects for the Fe and Ce or La electronic states near the interfaces in the multilayers.