Synthesis, crystal structure, and physical properties of $\mathrm{Yb}T\mathrm{Zn}$ ($T=\mathrm{Pd}$, Pt, and Au) and LuPtZn

We report the synthesis of three new Yb-based equiatomic compounds YbPdZn, YbPtZn, and YbAuZn, and of LuPtZn. According to the results of x-ray diffraction, these four compounds crystallize in the TiNiSi-type structure (orthorhombic $oP12\text{−}Pnma$, an ordered ternary variant of the ${\mathrm{Co}}_2\mathrm{Si}$ type). The Yb ions in YbPdZn and YbAuZn are in the divalent state, while a strong interplay of the single-ion Kondo and magnetic exchange interactions is observed in YbPtZn. The electrical resistivity of YbPtZn increases with decreasing temperature below $300\mathrm{K}$, peaks broadly around $45\mathrm{K}$, and decreases precipitously below $10\mathrm{K}$. A rapidly increasing $C_{4f}∕T$, where $C_{4f}$ is the $4f$-derived contribution to the heat capacity at low temperatures, indicates the onset of a heavy fermion state which orders magnetically at $1.35\mathrm{K}$; a reduced magnetic entropy of just $1.6\mathrm{J}∕\mathrm{mol}\mathrm{K}$ up to the ordering temperature indicates a small moment state in which the Yb-magnetic moment is appreciably screened by the Kondo interaction. The coefficient of the linear term in the electronic specific heat $\gamma$ obtained from extrapolating the zero-field data below $0.4\mathrm{K}\text{to}T=0\mathrm{K}$ in the magnetically ordered state is $0.75\mathrm{J}∕\mathrm{mol}{\mathrm{K}}^2$, showing a strongly renormalized electronic state due to the Kondo interaction. $\gamma$ decreases rapidly in applied magnetic fields due to the weakening of the Kondo interaction. The heat capacity and magnetoresistivity data indicate the presence of ferromagnetic correlations between the Yb ions. Such a feature is rare in Yb-based Kondo compounds.

Figure 1

The cubic root of the mean atomic volumes vs. the atom radii of the rare earths for the two series of equiatomic intermetallics $R\mathrm{Pd}\mathrm{Zn}$ and $R\mathrm{Pt}\mathrm{Zn}$ compounds.

Figure 2

Crystal structure of the $\mathrm{Yb}T\mathrm{Zn}$ phases $(T=\mathrm{Pd},\mathrm{Pt},\mathrm{Au})$, TiNiSi type; shown are the $T\text{−}\mathrm{Zn}$ sublattice and the Yb-Yb connections. Large circles, Yb; medium circles, Zn; small circles, Pd, Pt, or Au atoms.

Figure 3

The inverse susceptibility ${\chi }^{-1}$ of YbPtZn between 300 and $1.8\mathrm{K}$. The upper inset shows the susceptibility at low temperatures; lower inset shows magnetization at $1.8\mathrm{K}$ measured up to $7\mathrm{T}$.

Figure 4

The electrical resistivity of YbPtZn in zero and applied fields of 8 and $12\mathrm{T}$. The resistivity of LuPtZn in zero field and ${\rho }_{4f}$ $(={\rho }_{\mathrm{Yb}\mathrm{Pt}\mathrm{Zn}}-{\rho }_{\mathrm{Lu}\mathrm{Pt}\mathrm{Zn}})$ is also plotted. The inset shows ${\rho }_{4f}$ vs temperature at 0, 8, and $12\mathrm{T}$ below $10\mathrm{K}$. The solid lines are fits based on a linear variation of ${\rho }_{4f}$ with the temperature. The top panel shows the plot of ${\rho }_{4f}$ vs $\log \mathrm{T}$.

Figure 5

Normalized magnetoresistance $\rho \left(B\right)∕\rho \left(0\right)$ as a function of $B∕(T+T^{*})$ at 3, 4, 7, 10, and $20\mathrm{K}$ (see text for the meaning of $T^{*}$).

Figure 6

The heat capacity $C$ of YbPtZn down to $0.15\mathrm{K}$ in zero and various applied fields up to $8\mathrm{T}$. The inset shows $C∕T$ vs $T^2$ at 0, 2, and $8\mathrm{T}$.

Figure 7

The heat capacity of YbPtZn up to $20\mathrm{K}$ in zero and applied field of $8\mathrm{T}$. The heat capacity of LuPtZn is also plotted. $C_{4f}$ $(=C_{\mathrm{Yb}\mathrm{Pt}\mathrm{Zn}}-C_{\mathrm{Lu}\mathrm{Pt}\mathrm{Zn}})$ in 0 and $8\mathrm{T}$ is also shown. The entropy $S_{4f}$ obtained by integrating $C_{4f}∕T$ with respect to temperature is also shown.

Figure 8

The plots of Sommerfeld coefficient $\gamma$, average Yb magnetic moment, and the nuclear specific heat term $A_N$ as a function of magnetic field.

Figure 9

The thermal variation of the susceptibility of YbPdZn, YbAuZn, and LuPtZn, in the $300–1.8\mathrm{K}$ range. The inset shows magnetization up to $7\mathrm{T}$ at $1.8\mathrm{K}$.

Figure 10

Low temperature heat capacity of YbAuZn and YbPdZn, plotted as $C∕T$ vs $T^2$.

Figure 11

The electrical resistivity $\rho$ of YbAuZn and YbPdZn from 300 down to $1.7\mathrm{K}$.