57Fe Mossbauer spectrometry: A powerful technique to analyze the magnetic and phase characteristics in RE-Fe-B permanent magnets*

This review summarizes the recent advances on the application of Fe-57 Mossbauer spectrometry to study the magnetic and phase characteristics of Nd-Fe-B-based permanent magnets. First of all, the hyperfine structures of the Ce2Fe14B, (Ce, Nd)(2)Fe14B and MM2Fe14B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystal structure. The results show that the isomer shift delta and the quadrupole splitting Delta E-Q of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field B-hf increases monotonically with increasing Nd content and its value is influenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the low fraction secondary phases are determined by the Fe-57 Mossbauer spectrometry due to its high sensitivity. On this basis, the content, magnetic behavior, and magnetization of the REFe2 phase, the amorphous grain boundary (GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.

Automated summary

This review summarizes recent advances in using Fe-57 Mossbauer spectrometry to study the magnetic and phase characteristics of Nd-Fe-B-based permanent magnets. The study determines the hyperfine structures of specific phases and investigates the effects of low fraction secondary phases on magnetic properties in depth.