A Mössbauer effect study of the microscopic magnetic properties of Th2Fe17 and its nitride, Th2Fe17N2.6

Abstract

The Mössbauer spectra of Th₂Fe₁₇ and Th₂Fe₁₇N_2.6 have been measured at various temperatures between 85 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 Th₂Fe₁₇, the 85 K weighted average isomer shift increases from 0.037 to 0.156 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. The nonmagnetic thorium in Th₂Fe₁₇N_2.6 yields an easy axis of magnetization which, in contrast to magnetic rare earths in R₂Fe₁₇ and R₂Fe₁₇N_x, is in a general basal direction and not oriented along one of the basal axes. The isomer shift and its temperature dependence for both Th₂Fe₁₇ and its nitride are very similar to those observed in related rare‐earth R₂Fe₁₇ compounds and their nitrides. Upon nitrogenation of Th₂Fe₁₇, the 85 K weighted average hyperfine field increases from 256.3 to 336.5 kOe. However, the increases on the 6c and 18f sites are smaller than those observed on the 9d and 18h sites; changes which are in agreement with changes in the magnetic moments observed by neutron diffraction and calculated for the nitrogenation of Nd₂Fe₁₇, Gd₂Fe₁₇, and Y₂Fe₁₇.