"Double" Ferromagnetism inGd70Y30Single Crystals

Magnetic-susceptibility, electrical-resistivity, and specific-heat measurements on ${\mathrm{Gd}}_{70}$ ${\mathrm{Y}}_{30}$ single crystals show Curie-Weiss behavior down to a $T_{\mathrm{C}}$ of 218.8 K along both $c$ and $a$ axes. Below 218.8 K the $a$-axis sample shows a second (hence the term "double") Curie-Weiss behavior down to 205.5 K while the $c$-axis sample exhibits a constant magnetic moment. A model is proposed which places the Gd moments on a cone about the $c$ axis at 218.8 K with the random basal-plane component ordering subsequently at 205.5 K.