Electronic and magnetic structures of the rare-earth compounds ${\mathit{R}}_2$${\mathrm{Fe}}_{17}$${\mathrm{N}}_{\xi }$

Structural and magnetic properties of the rare-earth compounds ${\mathit{R}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_{\xi }$ have been studied with neutron-diffraction measurements and self-consistent spin-polarized electronic-structure calculations. The diffraction results indicate for the Nd compound that N goes into two sites in two or more phases of varying fractional N occupations. For the Y compound N occupies only one site. Electronic-structure calculations for ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_{17}$ and ${\mathrm{Y}}_2$ ${\mathrm{Fe}}_{17}$ ${\mathrm{N}}_3$ give excellent results for site-dependent Fe moments, and, with spin-fluctuation theory, explain the large change in the Curie temperature on nitrogenation.