Vanishing RKKY interactions in Ce-based cage compounds

TL;DR

This study investigates Ce-based cage compounds and finds that RKKY interactions vanish at low temperatures due to the ground state configuration, explaining the absence of long-range magnetic order.

Contribution

It demonstrates that the RKKY interaction vanishes in Ce$T_{2}$Cd$_{20}$ compounds with a $ extGamma_7$ ground state, providing insight into their magnetic behavior.

Findings

RKKY interactions vanish at low temperatures in these compounds.

The ground state of Ce$^{3+}$ ions is the $ extGamma_7$ doublet.

No long-range magnetic order observed down to millikelvin temperatures.

Abstract

We report the results of thermodynamic measurements in external magnetic field of the cubic Ce-based cage compounds Ce$T_{2}$Cd$_{20}$ ($T$ = Ni,Pd). Our analysis of the heat-capacity data shows that the $\Gamma_7$ doublet is the ground state multiplet of the Ce$^{3+}$ ions. Consequently, for the $\Gamma_7$ doublet it can be theoretically shown that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the localized Ce moments mediated by the conduction electrons, must vanish at temperatures much lower than the energy separating the ground state doublet from the first excited $\Gamma_8$ quartet. Our findings provide an insight as to why no long range order has been observed in these compounds down to temperatures in the millikelvin range.