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

K. Niitsu, A. Sato, T. T. Sasaki, R. Sawada, Y. Cho, Y. Takada, T. Sato, Y. Kaneko, A. Kato, T. Ohkubo, D. Shindo, K. Hono, Y. Murakami

    Research output: Contribution to journalArticlepeer-review

    24 Citations (Scopus)

    Abstract

    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.

    Original languageEnglish
    Pages (from-to)220-230
    Number of pages11
    JournalJournal of Alloys and Compounds
    Volume752
    DOIs
    Publication statusPublished - 2018 Jul 5

    Keywords

    • Coercivity
    • Grain boundary
    • Nd-Fe-B
    • Permanent magnets
    • Transmission electron microscopy

    ASJC Scopus subject areas

    • Mechanics of Materials
    • Mechanical Engineering
    • Metals and Alloys
    • Materials Chemistry

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