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

Abstract

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 $0.20\le x\le 0.75$, and both the Néel temperature, $T_{\text{N}}$, and the ordered magnetic moment per Ce, $\hat{I}¼$, linearly decrease with increasing $x$. The reduction in $\hat{I}¼$ points to strong hybridization of the increasingly diluted Ce $4f$ electrons, and we find a remarkable quadratic dependence of $\hat{I}¼$ 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.

Supplementary material included