Evolution of single-ion crystal field and Kondo features in Ce$_{0.5}$La$_{0.5}$Ni$_{9-x}$Cu$_x$Ge$_4$

TL;DR

This study investigates how substituting nickel with copper in a heavy fermion compound affects its magnetic interactions, revealing the persistence of Kondo shielding and the suppression of antiferromagnetic order at higher copper levels.

Contribution

It provides new insights into the evolution of crystal field and Kondo features in Ce-based compounds through substitution series analysis.

Findings

Single-ion scaling observed for low Cu concentrations.

Antiferromagnetic transition suppressed at higher Cu levels.

Kondo effect continues to shield 4f moments in CeNi8CuGe4.

Abstract

Starting with the heavy fermion compound CeNi$_9$Ge$_4$, the substitution of nickel by copper leads to a dominance of the RKKY interaction in competition with the Kondo and crystal field interaction. Consequently, this results in an antiferromagnetic phase transition in CeNi$_{9-x}$Cu$_x$Ge$_4$ for $x>0.4$, which is, however, not fully completed up to a Cu-concentration of $x=1$. To study the influence of single-ion effects on the AFM ordering by shielding the $4f$-moments, we analyzed the spin diluted substitution series La$_{0.5}$Ce$_{0.5}$Ni$_{9-x}$Cu$_x$Ge$_4$ by magnetic susceptibility $\chi$ and specific heat $C$ measurements. For small Cu-amounts $x\leq 0.4$ the data reveal single-ion scaling with regard to the Ce-concentration, while for larger Cu-concentrations the AFM transition (encountered in the CeNi$_{9-x}$Cu$_x$Ge$_4$ series) is found to be completely depressed. Calculation of the entropy reveal that the Kondo-effect still shields the 4$f$-moments of the Ce$^{3+}$-ions in CeNi$_8$CuGe$_4$.