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

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 $x^{\ast }\approx 0.6$. Tracking the temperature versus field history of the neutron depolarization, we find clear signatures of long-range Ising ferromagnetism below a Curie temperature $T_{\mathrm{C}}$ for $x=0.4$ and a spin freezing of tiny ferromagnetic clusters below a freezing temperature $T_{F1}$ for $x>x^{\ast }$. Under zero-field-cooling/field-heating and for $x>x^{\ast }$ a reentrant temperature dependence of the neutron depolarization between $T_{F2}<T_{F1}$ and $T_{F1}$ 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 $T_{F1}$ adjacent to a ferromagnetic quantum phase transition at $x^{\ast }$.