Electronic structure of $R\mathrm{AuMg}$ and $R\mathrm{AgMg}$ $(R=\mathrm{Eu},\mathrm{Gd},\mathrm{Yb})$

We have investigated the electronic structure of the equiatomic $\mathrm{EuAuMg}$, $\mathrm{GdAuMg}$, $\mathrm{YbAuMg}$, and $\mathrm{GdAgMg}$ intermetallics using x-ray photoelectron spectroscopy. The spectra revealed that the Yb and Eu are divalent while the Gd is trivalent. The spectral weight in the vicinity of the Fermi level is dominated by the mix of $\mathrm{Mg}s$, $\mathrm{Au}∕\mathrm{Ag}sp$, and $Rspd$ bands. We also found that the Au and $\mathrm{Ag}d$ bands are extraordinarily narrow, as if the noble metal atoms were impurities submerged in a low density $sp$ metal host. The experimental results were compared with band structure calculations, and we found good agreement provided that the spin-orbit interaction in the Au an $\mathrm{Ag}d$ bands is included and correlation effects in an open $4f$ shell are accounted for.

Figure 1

The two structures of the intermetallic $RT\mathrm{Mg}$ (from Ref. 5). On the left-hand side, the $\mathrm{ZrNiAl}$ structure which is adopted by the materials with trivalent rare earth and on the right-hand side, the $\mathrm{TiNiSi}$ structure for those with divalent rare earths.

Figure 2

(Color online) Experimental valence band photoemission spectra (left-hand panels) and calculated valence band density of states (right-hand panels) of polycrystalline $\mathrm{YbAuMg}$, $\mathrm{EuAuMg}$, $\mathrm{GdAuMg}$, and $\mathrm{GdAgMg}$ (from top to bottom).

Figure 3

Experimental valence band photoemission spectra of elemental Au (top panel) and Ag (bottom panel).

Figure 4

(Color online) Left-hand panels: experimental $\mathrm{Au}4f$ and $\mathrm{Ag}3d$ core level spectra of $\mathrm{YbAuMg}$, $\mathrm{EuAuMg}$, $\mathrm{GdAuMg}$, $\mathrm{GdAgMg}$, and elemental Au and Ag. Right-hand panels: simulated spectra based on the calculated $\mathrm{Au}4f$ and $\mathrm{Ag}3d$ energy positions.