Institute of Applied Physics, University of Hamburg
By applying spin-resolved scanning tunnelling spectroscopy at 0.3 K to a sample with Co nanostripes and single Co adatoms grown on a Pt(111) surface we probed the indirect magnetic exchange interactions between adatoms and nanostripes [1] and in pairs of adatoms [2]. We find that the interaction can be described as a Ruderman-Kittel-Kasuya-Yosida (RKKY)–like exchange which shows not only a distance but also a directional dependence on the atomic scale.
For host metals close to the onset of ferromagnetism (e.g. Pt, Pd) it is known that magnetic impurity atoms (e.g. Co, Fe) induce a spin-polarization of host atoms close to the impurity. These polarized host atoms exhibit a significant magnetic moment and form together with the magnetic impurity a so called giant moment system. A possible magnetic coupling between neighboring impurities provided by polarized host atoms depends on the extent of the polarization as well as on its decay. It is an interesting question how such an effect interferes with the RKKY-interaction.
We investigated how the polarization of Pt is influenced in the vicinity of Co nanostripes. Our results show that the Pt density of states shows a response to the stripe’s magnetic orientation. This response indicates an induced polarization within the Pt which exhibits an exponential decay and can be observed for distances larger than 1 nm from the stripe. Interestingly the measured RKKY interaction changes within this length scale from antiferromagnetic to ferromagnetic coupling
[1] F. Meier, L. Zhou, J. Wiebe, R. Wiesendanger, Science 320, 82 (2008)
[2] L. Zhou, J. Wiebe, S. Lounis, E. Vedmedenko, F. Meier, S. Blügel, P. H. Dederichs, and R. Wiesendanger, Nature Physics 6, 187 (2010)