Magnetic doping of a thiolated-gold superatom: First-principles density functional theory calculations

The ${\text{Au}}_{25}{\left(\text{SR}\right)}_{18}^{-}$ cluster is a new member in the superatom family which features a centered icosahedral shell $\left({\text{Au}}_{13}\right)$ protected by six $\text{RS}{\left(\text{AuSR}\right)}_2$ motifs (RS− being an alkylthiolate group). Here we show that this superatom can be magnetically doped by replacing the center Au atom with Cr, Mn, or Fe. We find that Cr- and Mn-doped clusters have an optimized magnetic moment of 5 Bohr magnetons while the Fe-doped cluster has an optimized magnetic moment of 3 Bohr magnetons. Although the dopant atom’s local magnetic moment makes a major contribution to the total moment, the icosahedral ${\text{Au}}_{12}$ shell is also found to be significantly magnetized. Our work here provides a scenario of magnetic doping of a metal-cluster superatom which is protected by ligands and made by wet chemistry.

Figure 1

(Color online) The $M@{\text{Au}}_{24}{\left(\text{SR}\right)}_{18}^{\text{q}}$ cluster from replacing the center Au atom of ${\text{Au}}_{25}{\left(\text{SR}\right)}_{18}^{-}$ with a dopant $M$. Au, light gray (green); S, dark gray (blue); $\text{R}-$, not shown.

Figure 2

Frontier spin orbital levels of $\text{Cr}@{\text{Au}}_{24}{\left({\text{SCH}}_3\right)}_{18}^{-}$.

Figure 3

(Color online) Spin-up orbitals of $\text{Cr}@{\text{Au}}_{24}{\left({\text{SCH}}_3\right)}_{18}^{-}$: (a) Highest occupied spin-up orbital; (b) the highest occupied spin-up orbital among the five $\text{Cr}d$-dominated levels (see Fig. 2).

Figure 4

(Color online) Isosurface plot of spin magnetization density of $\text{Cr}@{\text{Au}}_{24}{\left(\text{SR}\right)}_{18}^{-}$ (the isosurface is the center sphere whose isovalue is at 0.02 a.u.).