Ferro I phase and gadolinium

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-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