Absence of local magnetic moments in Ru and Rh impurities and clusters on Ag(100) and Pt(997)

The magnetism of quench-condensed Ru and Rh impurities and metal films on Ag(100) and Pt(997) has been studied using x-ray magnetic circular dichroism. In the coverage range between 0.22 and 2.0 ML, no dichroic signal was detected at the $M_{3,2}$ absorption edges of Ru on Ag(100) at a temperature of $5\mathrm{K}$ in the presence of an applied magnetic field. The same was found for coverages between 0.12 and 0.5 ML of Rh on Ag(100) and Pt(997). It is concluded that the magnetic moments of single impurities, small clusters of various shape, and monolayers of the $4d$ metals are below the detection limit of $0.04{\mu }_B$ per atom. These results provide an unambiguous determination of the local magnetic moment of Ru and Rh deposited on nonmagnetic transition-metal surfaces, which are in contrast with theoretical predictions.

Figure 1

$M_{3,2}$ XAS spectra of (a) Ru (0.22 ML), (b) Rh (0.09 ML) deposited on Ag(100), and (c) Rh (0.12 ML) on Pt(997) at $T=5\mathrm{K}$. The spectra were normalized to unity at the $M_3$ preedge energies. The background XAS measured prior to deposition on pristine Ag and Pt substrates is represented by dotted lines.

Figure 2

XAS and XMCD spectra of Ru on Ag(100) for coverages $0.22\pm 0.05$, $0.38\pm 0.05$, $1.1\pm 0.1$, and $2.0\pm 0.2$ ML, measured at $T=5\mathrm{K}$ and $B=5\mathrm{T}$. The XAS spectra are background subtracted. For clarity, the spectra have been offset in the vertical direction.

Figure 3

Histogram of the number of nearest neighbors (NNs) per adatom on a (100) fcc two-dimensional lattice for coverages of (a) 0.14 ML and (b) 0.22 ML assuming random adsorption (gray bars). Hatched bars represent the percentage of atoms included in a given cluster size $N$.

Figure 4

XAS and XMCD spectra of Rh on Ag(100) for coverages of $0.09\pm 0.05$, $0.14\pm 0.05$, $0.38\pm 0.1$, and $1.0\pm 0.1$ ML measured at $T=5\mathrm{K}$ and $B=6\mathrm{T}$. The XAS spectra are background substrated. For clarity, the spectra have been offset in the vertical direction.

Figure 5

XAS and XMCD spectra of Rh on Pt(997) for coverages of $0.12\pm 0.05$ and $0.22\pm 0.05$ ML measured at $T=5\mathrm{K}$ and $B=5\mathrm{T}$. The XAS spectra are background substrated. For clarity, the spectra have been offset in the vertical direction.