Ferro I phase and gadolinium

Abstract

Certain Gd alloys, such as Gd-Y, are known to exhibit an apparent ``double ferromagnetism'' in which the $c$ axis component orders on cooling from the paramagnetic phase $({T}_{C1})$, while the basal-plane component remains effectively paramagnetic. Subsequently the basal-plane component orders at a lower temperature $({T}_{C2})$. Our measurements of low-field ac susceptibility and magnetization for high-quality Gd and Gd-Y single crystals suggest that either the behavior originally used to identify ferro I, namely, the concave-upward growth of the $a$ axis moment in the approach on cooling to ${T}_{\text{SR}}$, is not necessarily an indicator of the phase, or that ferro I is also present in pure Gd. Of the several models that exist to describe ferro I, the results from this study favor the random-cone model.