A Mössbauer effect study of the microscopic magnetic properties of Nd2Fe17 and Nd2Fe17N2.6

Abstract

The Mössbauer spectra of Nd2Fe17 and Nd2Fe17N2.6 have been measured at various temperatures between 78 and 295 K and analyzed with a model that is based on the Wigner–Seitz cell environment of each iron site, the orientation of the magnetization, and the magnetic moments as determined from either neutron-diffraction measurements or band-structure calculations. Upon nitrogenation of Nd2Fe17, the weighted average isomer shift increases from 0.060 to 0.164 mm/s and further the isomer shifts of the four crystallographically distinct sites increase in agreement with the increase observed in their Wigner–Seitz cell volumes and the presence of a nitrogen near neighbor for two of the sites. Upon nitrogenation of Nd2Fe17, the weighted average hyperfine field increases from 292.3 to 333.8 kOe. However, the increases on the 6c and 18f sites are much smaller than those observed on the 9d and 18h sites; changes which are in agreement with calculated changes in the magnetic moments upon nitrogenation of Nd2Fe17, Gd2Fe17, and Y2Fe17. The temperature dependence of the isomer shifts indicates an increase in covalency upon the formation of the nitride.