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A Nd-Fe-O intergranular phase in Nd-Fe-B sintered magnets and its effect on coercivity

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4 Author(s)
Zhongmin Chen ; Dept. of Mater. Sci. & Eng., Xi'an Jiaotong Univ., China ; Naxin Wang ; Xiaoping Song ; Xiaotian Wang

The intergranular microstructure and coercivity of Nd richer Nd xFe93-xB7 (x=16-28) sintered magnets have been systematically studied by means of scanning electron microscopy, analytical transmission electron microscopy, scanning Auger multiprobe, thermomagnetic analysis, magnetic measurement and annealing experiments. A new stable Nd-Fe-O ferromagnetic phase with a composition NdFe2Ox (x≈0.3) and a Curie temperature of 145°C is found in the intergranular regions of the magnets, due to the introduction of a considerable amount of oxygen during magnet processing and its segregation in the intergranular regions. The phase forms at ~650°C and volume fraction reaches a maximum of ~4% in the Nd22Fe71B7 magnets. This new phase has a strong hindrance effect on the propagation of reversed domain walls between Nd2Fe14B grains, and thus leads to a considerable enhancement of coercivity. Raising the Curie temperature of this phase would be a new important approach to improve the high-temperature coercivity of Nd-Fe-B magnets

Published in:

IEEE Transactions on Magnetics  (Volume:31 ,  Issue: 3 )