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

Niitsu, Kodai; Sato, Atsuko; Sasaki, Taisuke; Sawada, Renshi; Cho, Y.; Takada, Yoko; Sato, T.; Kaneko, Yuji; Kato, Akira; Ohkubo, T.; Shindo, Daisuke; Hono, K.; Murakami, Yasukazu

doi:10.1016/j.jallcom.2018.04.055

Cited by 38 publications

(7 citation statements)

References 32 publications

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“…This is attributed to the fact that the electronic states of microstructure interfaces between the main phase and GB phases are responsible for the pinning effect to prevent the magnetization reversal caused by thermal fluctuation. 18,19) Recent investigations have demonstrated that doping of metallic elements such as Al, Co, Cu, and Ga greatly modifies the microstructure including the GB phase improving the coercivity. [20][21][22][23] In this sense, the atomic configurations and the magnetism of the GB phase is of significant importance.…”

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confidence: 99%

First-principles study of crystalline Nd–Fe alloys

Ainai

Tatetsu

Terasawa

et al. 2020

Appl. Phys. Express

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We report the crystal structure of Nd–Fe alloys as candidates for grain-boundary phases in Nd–Fe–B sintered magnets. We find that the crystal structure of the fluorite Nd–Fe alloys is stable for a wide composition range. We also demonstrate that solid solution of Ga is effective in stabilizing the fluorite crystal structure of Nd–Fe alloys, which is consistent with experimental observations reporting crystalline Nd–Fe alloys at the grain boundaries of Ga-added Nd–Fe–B permanent magnets.

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confidence: 99%

First-principles study of crystalline Nd–Fe alloys

Ainai

Tatetsu

Terasawa

et al. 2020

Appl. Phys. Express

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“…also [36] also reported these three types of the intergranular phases are nonferromagnetic using electron holography. Magneto-optical Kerr effect microscopy by Soderznik et al showed that the formation of thick non-ferromagnetic intergranular phase suppressed the cascade propagation of magnetic domains during the demagnetization process, which was considered to be responsible for the enhancement of coercivity [37].…”

Section: Why Is H C Of Sintered Magnets Only 02h a ?mentioning

confidence: 84%

Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets

Sepehri-Amin

Sasaki

et al. 2021

Science and Technology of Advanced Materials

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Physically, the coercivity of permanent magnets should scale with the anisotropy field of ferromagnetic compounds, H A ; however, the typical coercivity values of commercial polycrystalline sintered magnets are only ~0.2H A , which is known as Brown's paradox. Recent advances in multi-scale microstructure characterizations using focused ion beam scanning electron microscope (FIB/SEM), aberration corrected scanning transmission electron microscopy (C s -corrected STEM), and atom probe tomography (APT) revealed detailed microstructural features of commercial and experimental Nd-Fe-B magnets. These investigations suggest the magnetism of a thin layer formed along grain boundaries (intergranular phase) is a critical factor that influence the coercivity of polycrystalline magnets. To determine the magnetism of the thin intergranular phase, soft X-ray magnetic circular dichroism (XMCD) and electron holography played critical role. Large scale micromagnetic simulations using the models that are close to real microstructure incorporating the recent microstructure characterization results gave insights on how the coercivity and its thermal stability is influenced by the microstructures.Based on these new findings, coercivity of Nd-Fe-B magnets are being improved to its limit. This review replies to most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets based on our recent studies.

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“…Though the observance of this phase was extremely infrequent (only observed in two samples), the presence of any secondary phase detracting from the bulk magnetic properties as Nd 6 (Fe,Co) 13 Ga is antiferromagnetic. [50][51][52][53][54]…”

Section: Microstructure Through Different Processing Stagesmentioning

confidence: 99%

Direct Recycling of Hot‐Deformed Nd–Fe–B Magnet Scrap by Field‐Assisted Sintering Technology

Keszler,

Grosswendt,

Assmann

et al. 2023

Adv Energy and Sustain Res

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Recycling of Nd–Fe–B magnets is an ongoing challenge regarding circular economy. State‐of‐the‐art magnet production methods, such as hot deformation, have limitations with respect to direct recycling of magnet scrap particles that differ from pristine melt‐spun Nd–Fe–B powder. Recent work has shown that a combination of presintering by field‐assisted sintering technology/spark plasma sintering (FAST/SPS) and hot deformation by flash spark plasma sintering (flash SPS) has the potential to directly produce Nd–Fe–B magnets from 100% scrap material. Both processes have the capability to adjust and monitor process parameters closely, resulting in recycled magnets with properties similar to commercial magnets but made directly from crushed and recycled Nd–Fe–B powder that partially or completely replaces pristine melt‐spun Nd–Fe–B powder. Herein, a systematic study is done inserting recycled magnet particles into a flash SPS deformed magnet, considering the effects of different weight percentages of scrap material of varied particle size fractions. In some cases, coercivity HcJ of >1400 kAm−1 and remanence Br of 1.1 T can be achieved with 20 wt% scrap material. The relationship between particle size fraction, oxygen uptake, and percentage of recyclate in a final magnet are all explored and discussed with respect to magnets made from pristine material.

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

Cited by 38 publications

References 32 publications

First-principles study of crystalline Nd–Fe alloys

First-principles study of crystalline Nd–Fe alloys

Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets

Direct Recycling of Hot‐Deformed Nd–Fe–B Magnet Scrap by Field‐Assisted Sintering Technology

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