The change on the structural and magnetic properties of the Sm2Fe17 compound as the ratio of H-2/N-2 forming the mixture of the atmosphere in a plasma chamber used to nitride this compound varied, was investigated by Mossbauer spectroscopy and X-ray diffraction. Our results show that the increase of the hydrogen concentration in the mixed H-2/ N-2 atmosphere reduces the formation of the nitrogen-rich phases, Sm2Fe17N8 and Sm2Fe17N11 and increases the formation of the Sm2Fe17N3 phase, whose maximum values are obtained for 70% H-2 in the gas mixture. (C) 2003 Elsevier B. V. All rights reserved.