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The crystal structure and microstructure of Sm 2 (Fe 1 − x Ga x ) 17 ( x = 0−0.12) have been studied by X-ray diffraction and scanning electron microscopy analysis techniques. Results indicate that the alloys have a single phase with Th 2 Zn 17 -type structure for x ⩽ 0.02; when x = 0.05−0.12, two phases, namely Sm 2 (Fe, Ga) 17 and (Ga, Fe)Sm, exist and, the higher the gallium substitution the more (Ga, Fe)Sm phase occurs. The lattice parameters increase with Ga addition. The Curie temperature and saturation magnetization of the nitrides decrease with increasing gallium substitution; however, the anisotropy field reaches a maximum value of 18.4 T for x = 0.02 at room temperature. The hard magnetic properties of the nitrides decrease also except for x = 0.02. The optimum hard magnetic properties obtained are B r = 12.3 kG, i H c = 10.0 kOe and ( BH ) max = 26.2 MG Oe with x = 0.02. The thermomagnetic curves measured of all the nitrides have shown that the onset decomposition temperatures are 760–780 K, which are slightly affected by gallium substitution.

The intrinsic and hard magnetic properties of Sm 2 (Fe 1 − x Al x ) 17 nitrides were investigated. The Curie temperature and saturation magnetization decrease linearly with increasing Al concentration, as also does the anisotropy field at room temperature. The X-ray diffraction patterns have shown that all the samples exist in a nearly single phase with Th 2 Zn 17 -type structure for x up to 0.12. The lattice parameters increase with the substitution of Al for Fe atoms. The hard magnetic properties of the nitrides obtained indicate that the addition of Al has an unfavorable effect. The onset decomposition temperature of all nitrides derived from the thermomagnetic curves is around 750 K, implying that Al substitution could not improve the thermal stability of 2:17 nitrides.