Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 9: Surface Magnetism II
MA 9.2: Vortrag
Montag, 23. März 2009, 15:30–15:45, HSZ 403
Magnetic properties of Co and Fe on Pt(111), Rh(111) and Pd(111) : From single atoms to ultrathin films — •Anne Lehnert1, Stefano Rusponi1, Markus Etzkorn1, Géraud Moulas1, Pietro Gambardella2, Peter Bencok3, and Harald Brune1 — 1IPN, EPF-Lausanne, Switzerland — 2CREA and Catalan Institute of Nanotechnology, — 3ESRF, Grenoble, France
Single atoms of Co on Pt(111) are known to have a giant magnetic anisotropy energy (MAE) of 9.3 meV/atom [1]. This is due to the reduced coordination and the strong spin-orbit coupling of the Pt 5d-states. In order to study the contribution of a highly polarizable substrate to the MAE, we investigated single Co atoms on Pd(111) and Rh(111) using x-ray magnetic circular dichroism (XMCD). We find a decreasing MAE moving from a 5d-substrate (Pt) to 4d-substrates (Pd and Rh). Co has a large orbital moment L of about 0.7 independent of the substrate. The easy axis is out-of-plane for Pt(111) and Pd(111) whereas it is in-plane for Co/Rh(111). Fe has on all substrates an out-of-plane easy axis, a very small anisotropy energy, and a L/S ratio of about 0.1. With increasing coverage the coordination number of the adatom increases and generally leads to a reduced MAE and orbital moment compared to the single atom. We measure one monolayer of Co and Fe on Pt(111) and Rh(111) and find MAE values <0.5 meV/atom [2]. For 1 ML Co we find a substantial decrease in the L/S ratio to 0.19. However, the L/S ratio for 1 ML Fe on both substrates does not change much compared with the Fe single atom. [1] Gambardella et al., Science 300, 1130 (2003); [2] Moulas et al. PRB in press