Abstract
SmxFe100-x alloys with x = 11, 12, 12.5, 13 and 14 were synthesized by mechanical alloying (MA). It was found that with increasing annealing temperature from 600 to 900°C, the Curie temperature would decrease from 220 to 136°C which is still higher than that of as-melted and annealed Sm10.5Fe89.5. X-ray diffraction study indicated that the former tends to be of the TbCu7 structure and the latter is of the Th2Zn17 type. After nitrogenation, the Curie temperatures of two of these alloys were raised to about 480°C. High coercivities have been achieved in the nitrided samples. The best results obtained for the MA samples are iHc = 44.0 kOe, Br= 8.0 kG and (BH)max = 14.3 MGOe. High coercivities might originate from the SmFe7Nδ phase in the MA samples. Proper annealing is necessary to complete the solid state reaction for forming metastable phase SmFe7. It has been found that the optimum annealing temperature is 750°C. Too high annealing temperature leads to excessive loss of samarium. Transformation of SmFe7 to Sm2Fe17 occurs at 1000°C, resulting in the decrease of the coercivity.
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