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

TL;DR

This study investigates the magnetic and quantum critical behavior of CePd$_{1-x}$Rh$_x$ near ferromagnetic instability, revealing a Kondo-cluster-glass state and quantum Griffiths phase effects without a true quantum critical point.

Contribution

It provides the first comprehensive experimental evidence for a Kondo-cluster-glass state and quantum Griffiths phase in this heavy-fermion system near ferromagnetic quantum phase transition.

Findings

Identification of a Kondo-cluster-glass state for x ≥ 0.65

Absence of divergence in Grüneisen ratio as T→0

Non-Fermi-liquid effects consistent with quantum Griffiths phase

Abstract

We report on a comprehensive study of CePd$_{1-x}$Rh$_x$ $(0.6 \leq x \leq 0.95)$ 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 Gr\"uneisen 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 $x\geq 0.65$, and the NFL effects in the specific heat, ac susceptibility and magnetization are compatible with the quantum Griffiths phase scenario.