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Thermochemical copper coating for surface diffusion control and magnetic performance optimization in NdFeB permanent magnets.

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Title: Thermochemical copper coating for surface diffusion control and magnetic performance optimization in NdFeB permanent magnets.
Authors: Lo, Wen-Chih1 (AUTHOR), Mo, Chih-Chieh1 (AUTHOR), Huang, Ching-Chien1 (AUTHOR) huangcc@nkust.edu.tw
Source: International Journal of Modern Physics B: Condensed Matter Physics; Statistical Physics; Applied Physics. 4/20/2026, Vol. 40 Issue 9/10, p1-9. 9p.
Subjects: Surface diffusion, Permanent magnets, Magnetic properties, Grain refinement, Coercive fields (Electronics), Crystal grain boundaries, Copper surfaces, Copper films
Abstract: The performance of NdFeB permanent magnets is governed by the chemistry and continuity of their grain boundary phases, yet conventional copper modification often suffers from uncontrolled segregation that degrades coercivity. This study establishes a thermochemical coating strategy that enables precise regulation of copper surface diffusion through a combination of powder pretreatment and temperature-controlled heat processing. Vacuum pretreatment of commercially obtained copper citrate powder enhances its reactivity and produces a twofold increase in diffusion depth relative to untreated powder, as verified by glow discharge spectroscopy. Systematic temperature optimization further reveals that treatment at 600∘C generates the most uniform and effective Cu penetration, driven by liquid-phase-assisted transport above the Nd-Cu eutectic threshold. This optimized diffusion pathway forms a continuous Cu-enriched boundary layer while preventing excessive segregation. Magnetic measurements confirm that the intrinsic magnetic performance, including coercivity (iHc) and maximum energy product ((BH)max), is retained after diffusion, demonstrating that microstructural refinement is achieved without compromising the primary magnetic phase. The findings provide a reproducible and scalable pathway for grain boundary engineering in NdFeB magnets and establish an experimentally validated framework for coupling surface diffusion control with magnetic property stabilization. [ABSTRACT FROM AUTHOR]
Copyright of International Journal of Modern Physics B: Condensed Matter Physics; Statistical Physics; Applied Physics is the property of World Scientific Publishing Company and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
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Header DbId: egs
DbLabel: Engineering Source
An: 192376251
AccessLevel: 6
PubType: Academic Journal
PubTypeId: academicJournal
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  Data: Thermochemical copper coating for surface diffusion control and magnetic performance optimization in NdFeB permanent magnets.
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  Data: <searchLink fieldCode="AR" term="%22Lo%2C+Wen-Chih%22">Lo, Wen-Chih</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Mo%2C+Chih-Chieh%22">Mo, Chih-Chieh</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Huang%2C+Ching-Chien%22">Huang, Ching-Chien</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> huangcc@nkust.edu.tw</i>
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  Data: <searchLink fieldCode="DE" term="%22Surface+diffusion%22">Surface diffusion</searchLink><br /><searchLink fieldCode="DE" term="%22Permanent+magnets%22">Permanent magnets</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+properties%22">Magnetic properties</searchLink><br /><searchLink fieldCode="DE" term="%22Grain+refinement%22">Grain refinement</searchLink><br /><searchLink fieldCode="DE" term="%22Coercive+fields+%28Electronics%29%22">Coercive fields (Electronics)</searchLink><br /><searchLink fieldCode="DE" term="%22Crystal+grain+boundaries%22">Crystal grain boundaries</searchLink><br /><searchLink fieldCode="DE" term="%22Copper+surfaces%22">Copper surfaces</searchLink><br /><searchLink fieldCode="DE" term="%22Copper+films%22">Copper films</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: The performance of NdFeB permanent magnets is governed by the chemistry and continuity of their grain boundary phases, yet conventional copper modification often suffers from uncontrolled segregation that degrades coercivity. This study establishes a thermochemical coating strategy that enables precise regulation of copper surface diffusion through a combination of powder pretreatment and temperature-controlled heat processing. Vacuum pretreatment of commercially obtained copper citrate powder enhances its reactivity and produces a twofold increase in diffusion depth relative to untreated powder, as verified by glow discharge spectroscopy. Systematic temperature optimization further reveals that treatment at 600∘C generates the most uniform and effective Cu penetration, driven by liquid-phase-assisted transport above the Nd-Cu eutectic threshold. This optimized diffusion pathway forms a continuous Cu-enriched boundary layer while preventing excessive segregation. Magnetic measurements confirm that the intrinsic magnetic performance, including coercivity (iHc) and maximum energy product ((BH)max), is retained after diffusion, demonstrating that microstructural refinement is achieved without compromising the primary magnetic phase. The findings provide a reproducible and scalable pathway for grain boundary engineering in NdFeB magnets and establish an experimentally validated framework for coupling surface diffusion control with magnetic property stabilization. [ABSTRACT FROM AUTHOR]
– Name: AbstractSuppliedCopyright
  Label:
  Group: Ab
  Data: <i>Copyright of International Journal of Modern Physics B: Condensed Matter Physics; Statistical Physics; Applied Physics is the property of World Scientific Publishing Company and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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RecordInfo BibRecord:
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        Value: 10.1142/S0217979226400023
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      – Code: eng
        Text: English
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        PageCount: 9
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      – SubjectFull: Surface diffusion
        Type: general
      – SubjectFull: Permanent magnets
        Type: general
      – SubjectFull: Magnetic properties
        Type: general
      – SubjectFull: Grain refinement
        Type: general
      – SubjectFull: Coercive fields (Electronics)
        Type: general
      – SubjectFull: Crystal grain boundaries
        Type: general
      – SubjectFull: Copper surfaces
        Type: general
      – SubjectFull: Copper films
        Type: general
    Titles:
      – TitleFull: Thermochemical copper coating for surface diffusion control and magnetic performance optimization in NdFeB permanent magnets.
        Type: main
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          Name:
            NameFull: Lo, Wen-Chih
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            NameFull: Mo, Chih-Chieh
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            NameFull: Huang, Ching-Chien
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            – D: 20
              M: 04
              Text: 4/20/2026
              Type: published
              Y: 2026
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              Value: 40
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              Value: 9/10
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            – TitleFull: International Journal of Modern Physics B: Condensed Matter Physics; Statistical Physics; Applied Physics
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