Observation of a Griffiths-like phase in the paramagnetic regime of ErCo_2

TL;DR

This study provides evidence of a Griffiths-like phase in paramagnetic ErCo2, characterized by ferromagnetic clusters and susceptibility anomalies, revealed through x-ray dichroism, neutron scattering, and ac susceptibility measurements.

Contribution

It demonstrates the presence of a Griffiths-like phase in ErCo2, linking magnetic clusters and susceptibility features to this phenomenon in a paramagnetic regime.

Findings

Presence of ferromagnetic clusters in the paramagnetic phase

Loss of analyticity in magnetic susceptibility

High sensitivity of susceptibility to applied magnetic field

Abstract

A systematic x-ray magnetic circular dichroism study of the paramagnetic phase of ErCo2 has recently allowed to identify the inversion of the net magnetization of the Co net moment with respect to the applied field well above the ferrimagnetic ordering temperature, Tc. The study of small angle neutron scattering measurements has also shown the presence of short range order correlations in the same temperature region. This phenomenon, which we have denoted parimagnetism, may be related with the onset of a Griffiths-like phase in paramagnetic ErCo2. We have measured ac susceptibility on ErCo2 as a function of temperature, applied field, and excitation frequency. Several characteristics shared by systems showing a Griffiths phase are present in ErCo2, namely the formation of ferromagnetic clusters in the disordered phase, the loss of analyticity of the magnetic susceptibility and its extreme sensitivity to an applied magnetic field. The paramagnetic susceptibility allows to establish that the magnetic clusters are only formed by Co moments as well as the intrinsic nature of those Co moments.