Kondo-Cluster-Glass State near a Ferromagnetic Quantum Phase Transition

Abstract

We report on a comprehensive study of CePd${}_{1-x}$Rh${}_x$ $(0.6\le x\le 0.95)$ poly- and single crystals close to the ferromagnetic instability by means of low-temperature ac susceptibility, magnetization and volume thermal expansion. The signature of ferromagnetism in this heavy-fermion system can be traced from 6.6 K in CePd down to 25 mK for $x=0.87$. Despite pronounced non-Fermi-liquid (NFL) effects in both, specific heat and thermal expansion, the Grüneisen ratio {\it does not} diverge as $T\to 0$, providing evidence for the absence of a quantum critical point. Instead, a peculiar "Kondo-cluster-glass" state is found for $x\ge 0.65$, and the NFL effects in the specific heat, ac susceptibility and magnetization are compatible with the quantum Griffiths phase scenario.

4 pages, 4 figures