Plasma nitrogenation of Pr2Fe17 and Sm2Fe17

The effect of plasma nitrogenation on the structural and magnetic propertie s of Pr2Fe17 and Sm2Fe17 compounds was investigated by Mossbauer spectrosco py, thermomagnetic measurements, optical metallography, and electronic micr oprobe analysis. Samples were prepared starting from Pr2Fe17 and Sm2Fe17 co mmercial powders with 20 mu m granulometry, submitted to nitrogenation trea tment at 400 degrees C in 10 Torr atmosphere of 80%H-2-20%N-2 during period s up to 8 h. Our results show the formation of R2Fe17N3 and metallic Fe and indicate the existence of two other phases. The Mossbauer parameters of th e latter are characterized by magnetic hyperfine fields (peak values) of 21 (24) and 3 (4) T and isomer shifts of 0.17 and 0.24 (0.24 and 0.29) mm/s f or Pr (Sm). Their magnetic-phase transitions were determined to be close to 250 and 90 degrees C. Our results suggest that these 2:17 phases present s toichiometries close to R2Fe17N8 and R2Fe17N11, respectively. (C) 2000 Amer ican Institute of Physics. [S0021-8979(00)21908-7].