Magnetism of Rh and Ru atoms, clusters, and monolayers on Au and Ag surfaces

Abstract

The magnetic character of Rh and Ru on the surface of Au and Ag is investigated by means of weak localization (WL) and the anomalous Hall effect (AHE). Dephasing of the conduction electrons in WL is the most sensitive method to detect magnetic surface impurities. The Au/Rh and Au/Ru systems are investigated in the range between 1/100 of a monolayer of Rh (Ru) and several monolayers of Rh (Ru). We observe a small dephasing by Rh clusters and no dephasing by single Rh surface impurities, while single Ru surface impurities cause already a finite but small dephasing. We suggest that the dephasing is caused by small fluctuating magnetic moments of the order of 0.1 (0.4)${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$. For a coverage of one monolayer of Rh we observe a maximum in the dephasing. However, we do not observe a ferromagnetic Rh monolayer as predicted in a number of theoretical papers. Similarly, a Ru monolayer on the surface of Au or Ag does not show ferromagnetism. The absence of an AHE in the Rh and Ru monolayers excludes ferromagnetism as well. For Rh the dephasing increases again when the Rh coverage exceeds two monolayers, suggesting that pure bulk Rh shows spin fluctuations.