Crystal structure and Kondo lattice behavior ofCeNi9Si4

Abstract

We have studied the crystal chemistry and magnetic, thermodynamic, and transport properties of $R{\mathrm{Ni}}_{9}{\mathrm{Si}}_{4}$ with $R=\mathrm{La}$ and Ce. These compounds crystallize in a fully ordered tetragonal (space group $I4/mcm)$ variant of the cubic ${\mathrm{NaZn}}_{13}$ type. The low-temperature properties characterize ${\mathrm{CeNi}}_{9}{\mathrm{Si}}_{4}$ as a Kondo lattice with a large Sommerfeld value $\ensuremath{\gamma}=155(5){\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K}}^{2}$ as compared to $\ensuremath{\gamma}=33{\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K}}^{2}$ of Pauli paramagnetic ${\mathrm{LaNi}}_{9}{\mathrm{Si}}_{4}.$ The temperature dependencies of the specific heat and susceptibility are well described by the degenerate $(J=5/2)$ Coqblin-Schrieffer model with a characteristic temperature ${T}_{0}\ensuremath{\simeq}180\mathrm{K}.$ The large Ce-Ce spacing in ${\mathrm{CeNi}}_{9}{\mathrm{Si}}_{4}$ ${(d}_{\mathrm{C}\mathrm{e}\ensuremath{-}\mathrm{C}\mathrm{e}}\ensuremath{\approx}5.6\mathrm{\AA{}})$ implies very weak Ce-Ce intersite exchange interactions which is corroborated by the thermoelectric power $S(T)$ showing close agreement with theoretical results of the degenerate Anderson lattice without intersite interactions. ${\mathrm{CeNi}}_{9}{\mathrm{Si}}_{4}$ appears to be a model type Kondo lattice system with ${T}_{0}g{\ensuremath{\Delta}}_{\mathrm{CEF}}\ensuremath{\gg}{T}_{\mathrm{RKKY}}$ where ${T}_{0},$ ${\ensuremath{\Delta}}_{\mathrm{CEF}}$ (crystalline electric field), and ${T}_{\mathrm{RKKY}}$ (Ruderman-Kittel-Kasuya-Yosida) are the characteristic energy scales of the Kondo interaction, crystal field splitting, and Ce-Ce intersite exchange coupling, respectively. ${\mathrm{CeNi}}_{9}{\mathrm{Si}}_{4}$ shows a remarkably low ratio $A/{\ensuremath{\gamma}}^{2}=0.83(8)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\ensuremath{\mu}\ensuremath{\Omega}\mathrm{cm}(\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{K}/\mathrm{m}\mathrm{J}{)}^{2}$ which is one order-of-magnitude smaller than the usual Kadowaki-Woods ratio of heavy-fermion systems.