Neutron Depolarization due to Ferromagnetism and Spin Freezing in CePd$_{1-x}$Rh$_x$

TL;DR

This study uses neutron depolarization to investigate how ferromagnetism diminishes and spin freezing occurs in CePd$_{1-x}$Rh$_x$, revealing a transition to a Kondo-cluster glass state near a quantum phase transition.

Contribution

It provides the first microscopic evidence of the evolution from ferromagnetism to a Kondo-cluster glass in CePd$_{1-x}$Rh$_x$ around a critical Rh concentration.

Findings

Suppression of long-range ferromagnetism with increasing Rh content.

Observation of spin freezing and cluster growth at low temperatures.

Identification of a ferromagnetic quantum phase transition at x*.

Abstract

We report neutron depolarization measurements of the suppression of long-range ferromagnetism and the emergence of magnetic irreversibilities and spin freezing in CePd$_{1-x}$Rh$_x$ around $x^*\approx0.6$. Tracking the temperature versus field history of the neutron depolarization, we find clear signatures of long-range Ising ferromagnetism below a Curie temperature $T_{\rm C}$ for $x=0.4$ and a spin freezing of tiny ferromagnetic clusters below a freezing temperature $T_{\rm F1}$ for $x>x^*$. Under zero-field-cooling/field-heating and for $x>x^*$ a reentrant temperature dependence of the neutron depolarization between $T_{\rm F2}<T_{\rm F1}$ and $T_{\rm F1}$ is microscopically consistent with a thermally activated growth of the cluster size. The evolution of the depolarization as well as the reentrant temperature dependence as a function of Rh content are consistent with the formation of a Kondo-cluster glass below $T_{\rm F1}$ adjacent to a ferromagnetic quantum phase transition at $x^*$.