Anderson lattice in the intermediate valence compound Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$

We have studied magnetic, thermodynamic, and transport properties of Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ and its solid solution with the $T_c\simeq 13$ K superconductor La${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$. The solid solution (La,Ce)${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ reveals a rapid reduction of $T_c$ by increasing the Ce content with a complete suppression of superconductivity at the composition La${}_{2.85}$Ce${}_{0.15}$Ni${}_2$B${}_2$N${}_{3-\delta }$. The low-temperature properties characterize Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ as an intermediate valence system with a moderately enhanced Sommerfeld value $\gamma \simeq 54$ mJ/mol K${}^2$ and a susceptibility ${\chi }_0\simeq 1.6\times {10}^{-3}$ emu/mol, increased by about one order of magnitude as compared to the respective value ${\chi }_0\simeq 0.2\times {10}^{-3}$ emu/mol of superconducting La${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ ($\gamma =26$ mJ/mol K${}^2$) which serves as reference with a nonmagnetic rare earth ion. The electrical resistivity and thermoelectric power of Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ are analyzed in terms of the degenerate Anderson lattice model revealing a characteristic Kondo temperature $T_K^{\mathrm{ALM}}~1100$ K.

Figure 1

Measured room-temperature XRD pattern of LaCe${}_2$Ni${}_2$B${}_2$N${}_{3-\delta }$ and Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$. The solid lines derive from the Rietveld refinements. The strongest impurity line is marked by an asterisk.

Figure 2

Variation of the lattice parameters $a$ (circles) and $c$ (squares) (top panel) and unit cell volume (bottom panel) in the solid solution La${}_{3-x}$Ce${}_x$Ni${}_2$B${}_2$N${}_{3-\delta }$; lines are guides to the eye.

Figure 3

Temperature-dependent susceptibility for La${}_{3-x}$Ce${}_x$Ni${}_2$B${}_2$N${}_{3-\delta }$ measured at 1 mT (ZFC) with $x$ as labeled.

Figure 4

Specific heat of Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ (0 T) and La${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ (9 T) at selected temperatures. Inset: $C/T$ vs $T^2$ graph of the low-temperature part with solid lines indicating $C/T=\gamma +\beta T^2$ linear fits.

Figure 5

Temperature-dependent susceptibility of Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ and La${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ measured at applied fields of 1 T below 300 K and at 9 T above (a). Product of the Ce-$4f$ magnetic susceptibility with temperature $\chi T$ vs temperature (b). The solid line indicates the theoretical $\chi T$ of free Ce${}^{3+}$ ions.

Figure 6

The electrical resistivity $\rho (T)$ of Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ and La${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$. The solid line indicates a fit according to the ALM and the dashed line shows the normal metal ${\rho }_0+{\rho }_{\mathrm{BG}}$ contribution included in this fit. Inset: $\rho$ vs $T^2$ graph of the Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ data.

Figure 7

The electronic thermal resistance contributions estimated via the Wiedeman-Franz law from the electrical resistivity data and fitting by Eq. (2) (a). Temperature-dependent thermopower of Ce${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ and La${}_3$Ni${}_2$B${}_2$N${}_{3-\delta }$ (b). The solid line indicates the ALM fit (see text); dashed and dash-dotted lines are straight lines.