Microstructural insights into the coercivity enhancement of grain-boundary-diffusion-processed Tb-treated Nd-Fe-B sintered magnets beyond the core-shell formation mechanism

JOURNAL OF ALLOYS AND COMPOUNDS

卷:864

Article

Soderznik, Kristina Zagar¹  Rozman, Kristina Zuzek^1,8  Komelj, Matej¹  Kovacs, Andras^2,3  Diehle, Patrick^2,3  Denneulin, Thibaud^2,3  Savenko, Aleksei⁴  Soderznik, Marko⁵  Kobe, Spomenka^1,8  Dunin-Borkowski, Rafal E.^2,3  Mayer, Joachim^2,3,6  Markoli, Bostjan⁷  Sturm, Saso^1,8 

[1] Jozef Stefan Inst, Dept Nanostruct Mat, SI-1000 Ljubljana, Slovenia

[2] Forschungszentrum Julich, Ernst Ruska Ctr Microscopy & Spect Electrons, D-52425 Julich, Germany

[3] Forschungszentrum Julich, Peter Grunberg Inst, D-52425 Julich, Germany

[4] Forschungszentrum Julich, Cent Inst Engn Elect & Analit ZEA 3 Analyt, D-52425 Julich, Germany

[5] Univ Ljubljana, Fac Mech Engn, Lab Tribol & Interface Nanotechnol TINT, SI-1000 Ljubljana, Slovenia

[6] Rhein Westfal TH Aachen, Cent Facil Electron Microscopy, D-52056 Aachen, Germany

[7] Univ Ljubljana, Dept Mat & Met, Fac Nat Sci & Engn, SI-1000 Ljubljana, Slovenia

[8] Jozef Stefan Int Postgrad Sch, SI-1000 Ljubljana, Slovenia

关键词: Magnetism, Nd-Fe-B;    Grain-boundary diffusion;    Transmission electron microscopy;    Electron energy-loss spectroscopy;    Off-axis electron holography;    Atom-probe tomography;   

DOI  :  10.1016/j.jallcom.2021.158915

来源: Elsevier

【 摘 要 】

We propose a dominant core-shell formation mechanism for grain-boundary-diffusion-processed (GBDP), Tb-treated, Nd2Fe14B sintered magnets. A depth-sensitive analysis of Tb-treated samples, relative to a non-GBDP Nd2Fe14B magnet, showed a 30% increase of the coercivity in the central part of the magnet. A structure-chemistry-magnetic-property analysis revealed the dominant GBDP mechanism. On the surface of the Tb-treated magnet, the Tb is released from the starting precursor following a cascade of chemical reactions between the Tb oxide and the Nd and/or the Nd-Fe-B. The released Tb diffuses along the grain boundaries, forming a core-shell structure. The calculated optimum concentration for a 30% increase in the coercivity was 50 ppm of Tb. Off-axis electron-holography measurements were used to quantitatively map the characteristic magnetic states of the samples, confirming a different magnetic domain structure in the shell than in the core. The magnetic induction in the core was found to be 26% higher than that of the shell, which has a lower magnetic saturation due to the presence of Tb. The results show that the measured increase in the coercivity is due to a structural effect, and not the magnetic contribution of the Tb. Our results pave the way towards grain-boundary-engineering studies that can be used to increase the coercivity of Nd-Fe-B magnets for e-mobility and eco-power applications.

【 授权许可】

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