Structural and magnetic properties of Sm2Fe16MAl2 (M=Mn,Mo,Ni) and their carbides

Structural and magnetic properties of off-stoichiometric 2:17-type compounds Sm₂Fe₁₆MAl₂ (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 Th₂Zn₁₇ -type structure. When Mo was added into the parent compound Sm₂Fe₁₇Al₂, the unit cell was enlarged by 0.4%, larger than those of M=Ni, Mn. However, the Curie temperature T _c and saturation magnetization M_s of Sm₂Fe₁₆MoAl₂ 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 Sm₂Fe₁₆MAl₂, an increase in the volume of the unit cell and T_c, and a decrease of M_s were observed. The carbide of the parent had the largest cell dilation of 2.11%, which also exhibited relatively high T_c and M_s . When M=Ni, its carbide had the largest M_s, indicating that the addition of Ni had enhanced the ferromagnetic coupling. It was also found that Sm₂Fe₁₆MnAl₂C_1.5 was more stable than the other compounds, and that it decomposed at about 950°C