Reduction of the ordered-magnetic moment and its relationship to Kondo coherence in Ce${}_{1-x}$La${}_x$Cu${}_2$Ge${}_2$

The microscopic details of the suppression of antiferromagnetic order in the Kondo-lattice series Ce${}_{1-x}$La${}_x$Cu${}_2$Ge${}_2$ due to nonmagnetic dilution by La are revealed through neutron diffraction results for $x=0.20$, $0.40$, $0.75$, and $0.85$. Magnetic Bragg peaks are found for $0.20\le x\le0.75$,andboththeN\acute{e}eltemperature,$T_{$\text{N}$}$, and the ordered magnetic moment per Ce, $\mu$, linearly decrease with increasing $x$. The reduction in $\mu$ points to strong hybridization of the increasingly diluted Ce $4f$ electrons, and we find a remarkable quadratic dependence of $\mu$ on the Kondo-coherence temperature. We discuss our results in terms of local-moment- versus itinerant-type magnetism and mean-field theory, and show that Ce${}_{1-x}$La${}_x$Cu${}_2$Ge${}_2$ provides an exceptional opportunity to quantitatively study competing magnetic interactions in a Kondo lattice.