Amorphization of TbFe3 by nitrogen absorption

The nitrogenation process of the TbFe3 intermetallic compound was studied by heat treating the alloy between 573 and 873 K in a nitrogen atmosphere. The structural and magnetic properties of the nitrogenated samples were characterized by x-ray diffraction (XRD), Mössbauer spectroscopy, and magnetic measurements. The magnetic moments of the nitrogenated samples were found to be a function of the annealing temperature and showed a minimum for the sample heat treated at 673 K. The XRD pattern of this sample (673 K) showed that the Bragg peaks of the 1-3 phase had completely disappeared and were replaced by a broad maximum indicating a breakdown of the TbFe3 structure into an amorphous phase. The room-temperature Mössbauer spectrum of the same sample consisted almost entirely of a quadrupole-split doublet plus a small amount of α-Fe and TbFe3. This doublet split into a broad spectrum upon cooling which is typical of amorphous rare-earth–transition-metal compounds. For samples heat treated at higher temperatures, the amount of α-Fe and TbN phases gradually increased. This nitrogenation process is unlike that of R2Fe17. In this study, nitrogen atoms do not go into the interstitial sites. Instead, they create a ferromagnetic (TC≊215 K) amorphous phase of Tb, Fe, and N which is stable over a wide temperature range.