First Investiation of magnetic ground states in the rare-earth intermetallic compounds RAl$_{0.9}$Si$_{1.1}$ (R = Ce, Pr, Gd)

We report the magnetic properties strongly varying with the rare-earth elements in the newly found ternary compounds $R$Al$_{0.9}$Si$_{1.1}$, which crystallize in the tetragonal $alpha$-ThSi$_2$-type structure. For $R$ = Ce the alloy has a weak ferromagnetism below 11 K and for $R$ = Pr it orders ferromagnetically at 17 K, while for $R$ = Gd it is antiferromagnetic with $T_{rm N}$ = 30.5 K. In addition, we find no field effect on $T_{rm N}$ of $R$ = Gd because of the large internal mean field, but significant changes in the magnetic properties of $R$ = Ce and Pr.