Veranstaltungsdetails

26.1.2006, 15:30
Jungiusstr. 9, Hörsaal III

SFB 668 - Seminar

Dr. Oswald Pietzsch (IAP, Uni Hamburg):

Spin-Polarized Scanning Tunneling Spectroscopy of Co Islands on Cu(111)

The material pair Co and Cu is prototypical for a combination of magnetic and non-magnetic metallic substances. Exciting phenomena have been studied in Co-Cu systems, like the giant magneto-resistance effect in multilayer structures, or the many-particle Kondo interaction observed at individual Co adsorbates on a Cu surface. In my talk, I will present a low-temperature spinpolarized scanning tunneling microscopy/spectroscopy study of nanometer-sized Co islands on the Cu(111) face. These islands are ferromagnetic at 13 K with a strong perpendicular anisotropy [1]. Tunneling spectra reveal a particularly rich variety of features depending on structural properties like island stacking as well as on the spin state. In particular, the spin polarization strongy depends on energy, with its sign reversed several times in the observed energy interval. Experimental spectra will be interpreted with the aid of ab initio spin density calculations. As is well known, the Cu(111) surface exhibits a standing wave pattern due to surface state electrons scattered at step edges and other defects. A similar pattern can be observed on the Co islands [2]. It will be discussed how the patterns are affected by confinement to the triangular island geometry and by the spin character of the responsible dispersive state.

[1] O. Pietzsch, A. Kubetzka, M. Bode, and R. Wiesendanger, Phys. Rev. Lett. 92, 057202 (2004).
[2] L. Diekhoner, M.A. Schneider, A.N. Baranov, V.S. Stepanyuk, and K. Kern, Phys. Rev. Lett. 90, 236801 (2003).