Effect of Magnetic Field and Oxygen Pressure on the Decomposition of Sm ₂ Fe ₁₇ N ₃ Probed Using ⁵⁷ Fe Mössbauer Spectroscopy

The decomposition behavior of Sm 2 Fe 17 N 3 was investigated under flowing and static high‐purity oxygen with and without an applied magnetic field of 5 T. Under flowing oxygen at 100 Pa, the Sm 2 Fe 17 N x (0 < x ≦ 3) phase progressively decomposed with increasing heat‐treatment temperature, accompanied by the formation of α ‐Fe and iron oxides. Under static oxygen, little decomposition occurred at 100 Pa, whereas decomposition proceeded at 1000 Pa with increasing heat‐treatment time. It is noteworthy that α ‐Fe increased markedly, while iron oxides were not clearly detected even after prolonged heat treatment. Instead, Sm oxide was formed together with α ‐Fe, suggesting that local oxygen depletion developed during the reaction and suppressed further oxidation of Fe. These results demonstrate that an oxygen atmosphere strongly controls the decomposition pathway of Sm 2 Fe 17 N 3 , and that selective decomposition into Sm oxide and α ‐Fe can be achieved under static oxygen conditions. This finding provides a promising basis for an environmentally benign dry recycling process for Sm–Fe–N‐based magnets. The magnetic‐field effect was limited, indicating that the decomposition process was governed mainly by the chemical driving force of oxygen, while the magnetic contribution was secondary.