A neutron diffraction and Mössbauer effect study of the magnetic properties of Pr2Fe17 and Pr2Fe17N2.6

Abstract

The neutron diffraction powder patterns of Pr₂Fe₁₇ and Pr₂Fe₁₇N_2.6 have been measured at 295 K and refined within the Th₂Zn₁₇ structure type to give the structural changes which occur upon nitrogenation; changes which include a 6.4% expansion of the unit cell volume. The Mössbauer spectra of Pr₂Fe₁₇ and Pr₂Fe₁₇N_2.6 have been measured between 85 and 295 K and analyzed with a model which is based on the Wigner–Seitz cell environment of each iron site, the basal orientation of the magnetization, and a comparison with the Mössbauer spectra of Nd₂Fe₁₇ and Nd₂Fe₁₇N_2.6. Upon nitrogenation of Pr₂Fe₁₇, the 85 K‐weighted average isomer shift increases from 0.049 to 0.156 mm/s, and the isomer shifts of the four crystallographically distinct iron sites increase in agreement with the increase found in their Wigner–Seitz cell volumes and the presence of a nitrogen near‐neighbor for the 18f and 18h sites. The temperature dependence of the isomer shifts indicates an increase in covalency upon the formation of the nitride. Upon nitrogenation of Pr₂Fe₁₇, the 85 K‐weighted average hyperfine field increases from 286.2 to 331.9 kOe, however, as is the case for the nitrogenation of Nd₂Fe₁₇, the increases on the 6c and 18f sites are much smaller than those observed on the 9d and 18h sites. These changes provide support for the band structure calculations of changes in the magnetic moments upon nitrogenation of Y₂Fe₁₇, Nd₂Fe₁₇, and Gd₂Fe₁₇.