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

• Published in: Acta materialia Vol. 71; pp. 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: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.06.2014; Elsevier
• 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; Permanent magnets; Nanostructure; Transmission electron microscopy; Coercivity; Grain boundary; Coercive force; Permanent magnet; Microstructure; Magnetic properties
• ISSN: 1359-6454; 1873-2453
• DOI: 10.1016/j.actamat.2014.03.013

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.