The origin of the enhancement of magnetic properties in Sm2Fe17Nx (0<x≲3)

The Sm2Fe17Nx (1.2<x<2.1) of intermediate nitrogen contents prepared by a new method of nitrogenation were investigated about the hyperfine fields (HFs) at each Fe sites. The Mossbauer spectra of the samples could be analyzed as the superposition of spectra of the Sm2Fe17, the Sm2Fe17N3 and a small component with the HF of 5 T. The fractions of the phases depend on the nitrogen contents and the annealing durations. No intermediate HF was detected in the samples of x=1.1–2.1 regardless of the annealing duration. With the crystal structural consideration of the Th2Zn17 structure, the intermediate nitrogen content regions that could be detected by the X-ray diffraction and the magnetization measurements, should be magnetically composed of the mixtures of Fe–N and/or Fe–Fe–N hybridizations whose numbers are smaller than the case of Sm2Fe17N3. The chemical bonds formation in the system should be an important factor for the enhancement of the magnetic properties with nitrogen uptake, contrary to the facts expected and understood in the previous studies.