STRESS-INDUCED MAGNETIZATION IN PR2FE17NX COMPOUNDS

The dependence on x of the phases present in Pr2Fe17Nx powder particle s nitrided at 400 degrees C is studied by means of Mossbauer spectrosc opy. The results are compared with thermomagnetic analysis data and co nfirm the formation of a nitrogen-saturated core, as discussed in the literature, which is attributed to the diffusion of nitrogen through e xtended defects. The occurrence of three distinct Mossbauer subspectra is associated with the presence of the nitrogen-saturated phase with x = (2.8 +/- 0.2), the original binary phase and a volume fraction of the Pr2Fe17 phase which becomes magnetic at room temperature due to th e lattice expansion provoked by a stress-strain field within the parti cles. A model for the partially nitrided particles is employed success fully to account for the changes in the subspectral areas as well as t he approach to saturation observed in the average hyperfine field of s amples with nitrogen contents as low as x = 1.5; it also produces a pr eliminary value for the Poisson ratio (mu = 0.2) of the Pr2Fe17 phase.