Structural and magnetic properties of Sm/sub 2/Fe/sub 16/MAl/sub 2/ (M=Mn,Mo,Ni) and their carbides

Structural and magnetic properties of off-stoichiometric 2:17-type compounds Sm/sub 2/Fe/sub 16/MAl/sub 2/ (M=Mn,Mo,Ni) and their carbides were studied using X-ray powder diffractometry, magnetization measurement, thermomagnetic analysis, and differential thermal analysis. All these compounds had the Th/sub 2/Zn/sub 17/-type structure. When Mo was added into the parent compound Sm/sub 2/Fe/sub 17/Al/sub 2/, the unit cell was enlarged by 0.4%, larger than those of M=Ni, Mn. However, the Curie temperature T/sub c/ and saturation magnetization M/sub s/ of Sm/sub 2/Fe/sub 16/MoAl/sub 2/ were lower than the parent because the Mo atom had not effectively increased the separation of Fe-Fe pairs. When C was added to the parent and the Sm/sub 2/Fe/sub 16/MAl/sub 2/, an increase in the volume of the unit cell and T/sub c/, and a decrease of M/sub s/ were observed. The carbide of the parent had the largest cell dilation of 2.11%, which also exhibited relatively high T/sub c/ and M/sub s/. When M=Ni, its carbide had the largest M/sub s/, indicating that the addition of Ni had enhanced the ferromagnetic coupling. It was also found that Sm/sub 2/Fe/sub 16/MnAl/sub 2/C/sub 1.5/ was more stable than the other compounds, and that it decomposed at about 950/spl deg/C.