Magnetism of ultrathin intergranular boundary regions in Nd–Fe–B permanent magnets

The magnetism of a thin grain-boundary (GB) phase that envelopes the Nd2Fe14B grains in optimally annealed Nd–Fe–B sintered magnets was investigated by electron holography. The phase shift measured from a thin-foil specimen containing a tilted amorphous GB phase (∼3nm in width) was −0.34rad, which i...

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Bibliographic Details
Published in:Acta materialia 2014-06, Vol.71, p.370-379
Main Authors: Murakami, Y., Tanigaki, T., Sasaki, T.T., Takeno, Y., Park, H.S., Matsuda, T., Ohkubo, T., Hono, K., Shindo, D.
Format: Article
Language:English
Subjects:
Applied sciences
Coercivity
Exact sciences and technology
Ferrous alloys
Grain boundary
Grains
Magnetic materials
Magnetism
Magnets
Metals. Metallurgy
Nanostructure
Permanent magnets
Phase shift
Propagation
Sintering
Transmission electron microscopy
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Summary:The magnetism of a thin grain-boundary (GB) phase that envelopes the Nd2Fe14B grains in optimally annealed Nd–Fe–B sintered magnets was investigated by electron holography. The phase shift measured from a thin-foil specimen containing a tilted amorphous GB phase (∼3nm in width) was −0.34rad, which is substantially smaller than that expected for the nonferromagnetic GB phase of −1.2rad. Simulations of the phase shift with various magnetization values suggest that the magnetic flux density of the GB phase is ∼1.0T. The observations imply significant exchange coupling between Nd2Fe14B grains, which can explain the avalanche propagation of magnetization reversal observed in sintered magnets.
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2014.03.013