Dichroism in angular resolved VUV-photoemission from the (0001) surfaces of thin Gd and Nd films epitaxially grown on W(110)

We present investigations of the electronic and magnetic structure of the Rare Earth valence states. In particular, we have examined ultra thin films (≤ 10 ML) of the rare earth metals gadolinium and neodymium epitaxially grown on tungsten (110). Various experiments on dichroism in angular resolved photoemission have been performed using circularly as well as linearly polarised light in the VUV-range with photon energies below 40 eV. A special emphasis was placed on the investigation of the surface state, which was observed for both Gd and Nd. A very small magnetic splitting of about 25 meV was observed for the surface state of ferromagnetic Gd. A magnetic ordering of a Nd-monolayer on a remanently magnetised Fe-film is observed. Large dichroism effects are found for the surface state as well as the valence bands of paramagnetic Nd. In the latter case, these are used to determine the dispersion of the valence bands. Different numerical approaches are presented, one based on atomic photoionisation theory, another is based on a one-step model of solid state photoemission. Atomic photoionisation theory is used together with three-step calculations to explain the non-magnetic circular dichroism observed in the Gd 4f emission. The capability of dichroism experiments for resolving details of the electronic structure and for sensitive tests of photoemission calculations is demonstrated. Copyright Società Italiana di Fisica, Springer-Verlag 1999