Magnetization measurements for grain boundary phases in Ga-doped Nd-Fe-B sintered magnet

The magnetism of grain boundary (GB) phases in the Nd-rich Ga-doped Nd-Fe-B sintered magnet that shows unusually high improvement in coercivity by post-sinter optimal heat treatment was studied using electron holography. Transmission electron microscopy observations identified three types of GB phas...

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Bibliographic Details
Published in:Journal of alloys and compounds 2018-07, Vol.752, p.220-230
Main Authors: Niitsu, K., Sato, A., Sasaki, T.T., Sawada, R., Cho, Y., Takada, Y., Sato, T., Kaneko, Y., Kato, A., Ohkubo, T., Shindo, D., Hono, K., Murakami, Y.
Format: Article
Language:English
Subjects:
Coercivity
Ferrous alloys
Grain boundaries
Grain boundary
Heat exchange
Heat treatment
Holography
Magnetic fields
Magnetic flux
Magnetic materials
Magnetism
Magnets
Nd-Fe-B
Neodymium
Optimization
Permanent magnets
Phases
Sintering
Transmission electron microscopy
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Summary:The magnetism of grain boundary (GB) phases in the Nd-rich Ga-doped Nd-Fe-B sintered magnet that shows unusually high improvement in coercivity by post-sinter optimal heat treatment was studied using electron holography. Transmission electron microscopy observations identified three types of GB phases with distinct structures, i.e., Ia3¯-type, amorphous-type, and Nd6(Fe,Ga)14-type. The magnetic flux densities of these three GB phases were systematically analyzed by measuring the phase shifts of incident electrons, and all of these GB phases are concluded to be nonferromagnetic. Unlike the standard commercial sintered magnets, this study has shown that the Nd2Fe14B grains in the optimally heat treated Nd-rich Ga-doped sintered magnet are exchange decoupled by the formation of the three types of nonferromagnetic GB phases. The observations provide useful information for GB engineering of Nd-Fe-B sintered magnets, which is key for further improvements of their coercivities without relying on grain size refinement. [Display omitted] •Magnetization of the grain boundary phases in Ga-doped Nd-Fe-B magnet was studied.•Three types of grain boundary phases were observed in this sintered magnet.•Electron holography revealed that the grain boundary phases were nonferromagnetic.•The result provides useful information for the grain boundary engineering of sintered magnets.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2018.04.055