Intrinsic orbital and spin magnetism in Rh clusters on inert xenon matrices

Intrinsic orbital and spin magnetic moments of quasifree Rh clusters on inert xenon buffer layers are measured using x-ray magnetic circular dichroism. The moments strongly vary as a function of average cluster size. A maximum total moment of $0.4{\mu }_{\text{B}}$ per atom and large orbital-to-spin moment ratios up to 60% appear for ${\text{Rh}}_N$ clusters with average size $\overline{N}=20$, suggesting that cluster geometries are biplanar. The magnetism is further studied between two extreme limits, from quasifree few-atom-sized clusters situated on a xenon layer toward Rh nanostructures in contact with a weakly interacting Ag(100) substrate. Density-functional theory calculations for different cluster sizes and Rh-Ag coordination explain the unexpected quenching of Rh moments in the case of directly deposited Rh on Ag(100) reported by Honolka et al. [Phys. Rev. B 76, 144412 (2007)].

Figure 1

(Color online) (a) Measurement setup. (b) $\text{Rh}{M}_{3,2}$ TEY spectra for $\left(0.16\pm 0.05\right)\text{ML}$ Rhodium on xenon/Ag(100) $\left(T=10\text{K}\right)$. The dotted line shows the xenon/Ag(100) background. (c) Background subtracted XAS and XMCD (d) XMCD spectra in opposite field polarities $B=\pm 5\text{T}$.

Figure 2

(Color online) (a) Calculated average effective spin $\left({\mu }_{\text{S}}^{\prime }\right)$ and orbital moment $\left({\mu }_{\text{L}}\right)$ per hole and atom for different Rh coverages $\Theta$. (b) Measured XMCD/XAS asymmetry evaluated at the $M_3$ edge (495 eV). (c) Orbital-to-spin moment ratios.

Figure 3

(Color online) (a) XAS and (b) XMCD spectra for 0.12 ML Rh/Xe versus annealing temperature $T_{\text{a}}$. The inset (c) shows the peak at the $M_3$ edge, which shifts toward higher energies for increasing temperatures. (d) Extracted effective spin and orbital moments per hole and atom versus $T_{\text{a}}$.

Figure 4

(Color online) (a) Measured $\text{Rh}{M}_{3,2}$ XAS of Rh/xenon and Rh deposited on Ag(100) (from Ref. 6). For comparison bulk Rh is shown. (b) Calculated XAS spectra: (upper panel) free ${\text{Rh}}_{43}$ and ${\text{Rh}}_{19}$ clusters and bulk Rh, (lower panel) 2D ${\text{Rh}}_4$ clusters on top of Ag(100), embedded, and buried.