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Influence of defect thickness on the angular dependence of coercivity in rare-earth permanent magnets

Bance, S. and Oezelt, H. and Schrefl, T. and Ciuta, G. and Dempsey, N. M. and Givord, D. and Winklhofer, M. and Hrkac, G. and Zimanyi, G. and Gutfleisch, O. and Woodcock, T. G. and Shoji, T. and Yano, M. and Kato, A. and Manabe, A. (2014):
Influence of defect thickness on the angular dependence of coercivity in rare-earth permanent magnets.
In: Applied Physics Letters, AIP Publishing LLC, p. 182408, 104, (18), ISSN 0003-6951,
[Online-Edition: http://dx.doi.org/10.1063/1.4876451],
[Article]

Abstract

The coercive field and angular dependence of the coercive field of single-grain Nd2Fe14B permanent magnets are computed using finite element micromagnetics. It is shown that the thickness of surface defects plays a critical role in determining the reversal process. For small defect thicknesses reversal is heavily driven by nucleation, whereas with increasing defect thickness domain wall de-pinning becomes more important. This change results in an observable shift between two well-known behavioral models. A similar trend is observed in experimental measurements of bulk samples, where an Nd-Cu infiltration process has been used to enhance coercivity by modifying the grain boundaries. When account is taken of the imperfect grain alignment of real magnets, the single-grain computed results appears to closely match experimental behaviour.

Item Type: Article
Erschienen: 2014
Creators: Bance, S. and Oezelt, H. and Schrefl, T. and Ciuta, G. and Dempsey, N. M. and Givord, D. and Winklhofer, M. and Hrkac, G. and Zimanyi, G. and Gutfleisch, O. and Woodcock, T. G. and Shoji, T. and Yano, M. and Kato, A. and Manabe, A.
Title: Influence of defect thickness on the angular dependence of coercivity in rare-earth permanent magnets
Language: English
Abstract:

The coercive field and angular dependence of the coercive field of single-grain Nd2Fe14B permanent magnets are computed using finite element micromagnetics. It is shown that the thickness of surface defects plays a critical role in determining the reversal process. For small defect thicknesses reversal is heavily driven by nucleation, whereas with increasing defect thickness domain wall de-pinning becomes more important. This change results in an observable shift between two well-known behavioral models. A similar trend is observed in experimental measurements of bulk samples, where an Nd-Cu infiltration process has been used to enhance coercivity by modifying the grain boundaries. When account is taken of the imperfect grain alignment of real magnets, the single-grain computed results appears to closely match experimental behaviour.

Journal or Publication Title: Applied Physics Letters
Volume: 104
Number: 18
Publisher: AIP Publishing LLC
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 17 Nov 2014 09:08
Official URL: http://dx.doi.org/10.1063/1.4876451
Identification Number: doi:10.1063/1.4876451
Funders: We acknowledge the financial support from the Technology Research Association of Magnetic Materials for High Efficient Motors (MagHEM).
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