Neutron powder diffraction of rhombohedral ${\mathrm{Y}}_2$${\mathrm{Fe}}_{17}$ and ${\mathrm{Y}}_2$${\mathrm{Fe}}_{17}$${\mathrm{N}}_{3.1}$

High resolution neutron powder diffraction experiments were carried out on rhombohedral ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_{17}$ and the nitride ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_{3.1}$ at 10 K. The diffraction data were analyzed by the recently refined Rietveld method. The results obtained indicate that nitrogen atoms fully occupy the 9e site (99.5%) and that a small amount of N atoms locate at the 18g site (3.9%). The introduction of N atoms into ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_{17}$ leads to strong modification of the Fe magnetic moments. The magnetic moment of the 18f-Fe atoms which are the nearest to the 9e-N atoms in nitride is the lowest value (∼2.0${\mathrm{\mu }}_{\mathrm{B}}$), whereas the 6c-Fe atoms being the farthest from the 9e-N atoms have the highest moment (∼2.9${\mathrm{\mu }}_{\mathrm{B}}$). The difference of Fe moments on nonequivalent sites is discussed on the basis of the Fe-Fe and Fe-N bond distances. The obtained results are compared with the results of electronic band-structure calculation.