Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 28: Surface Magnetism

MA 28.15: Talk

Thursday, March 29, 2007, 18:45–19:00, H23

Intrinsically nonmagnetic surface on a magnetic bulk: Sm(0001) vs. Eu/Gd(0001) — •Daniel Wegner and Günter Kaindl — Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, 14195 Berlin

Samarium is a lanthanide metal with unusual electronic structure: While the bulk is trivalent with five electrons in the 4f shell, the (0001) surface is known to be divalent (six 4f-electrons). According to Hund's rule, spin and orbital moment cancel each other. This opens the possibility of a nonmagnetic surface layer, whereas the trivalent bulk is antiferromagnetic. We performed cryogenic scanning tunneling microscopy and spectroscopy on a thin Sm(0001) film grown on a W(110) single crystal. STM reproduces the well known hexagonal surface reconstruction. STS reveals a so far unknown unoccupied surface state that is not exchange-split. We interpret this as evidence that the surface layer is nonmagnetic. We compare the results with the electronically similar monolayer Eu/Gd(0001) that is known to couple ferromagnetically to the Gd substrate. Also the divalent Eu monolayer exhibits an unoccupied surface state. However, this state is clearly exchange-split due to the ferromagnetic ordering of the surface layer with non-vanishing magnetic moment.