A Mössbauer effect study of the Re2Fe14B magnets, where RE is Y, Pr, Nd, and Gd

Abstract

The Mossbauer spectra of Pr2Fe14B and Gd2Fe14B have been measured from 85 to 295 K and fit with a second order approximation in which the angle, ϕ, between the principal axis of the electric field gradient and the easy-axis of magnetization has been fixed by the positions of the near-neighbor rare-earth atoms. The coordination environment for each of the six iron sites in these materials has been determined from the Wigner-Seitz cell and used in the spectral analysis. The hyperfine parameters resulting from the above fit are in agreement with the structural and electronic properties of these compounds and also agree well with those determined in our earlier studies of Nd2Fe14B and Y2Fe14B. The magnetic hyperfine fields for the different sites are similar in the Y, Pr, and Nd compounds but are, as expected, higher in the Gd compound because of the much higher spin-multiplicity associated with Gd. The hyperfine fields on the 8j 1 and 4c sites, which have the most rare-earth near-neighbors show, as expected, the largest variation with rare-earth atom. The quadrupole interactions are constant with temperature and the absolute value of the quadrupole interactions on the 8j 2 and 4e site are found to be the largest, as is consistent with the highly distorted environment of these sites With the possible exception of the 4c site, the quadrupole interaction shows little variation with rare-earth atom. The isomer shift for each site in each compound varies linearly with temperature, as expected, for the second-order Doppler shift and gives effective Mossbauer masses between 62 and 67 g/mole. The weighted average isomer shift is similar in each of these compounds, but the isomer shifts associated with some of the specific sites in Gd2Fe14B are rather different than in the Y, Pr, and Nd compounds.