Observation of a Griffiths-like phase in the paramagnetic regime of ErCo(2)

A systematic x-ray magnetic circular dichroism study of the paramagnetic phase of ErCo(2) has recently allowed us 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, T(c). 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 to the onset of a Griffiths-like phase in paramagnetic ErCo(2). We have measured ac susceptibility on ErCo(2) as a function of temperature, applied field and excitation frequency. Several characteristics shared by systems showing a Griffiths phase are present in ErCo(2), 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 us to establish that the magnetic clusters are only formed by Co moments as well as the intrinsic nature of those Co moments.