Strategy for high-coercivity Nd–Fe–B magnets

Hono, K.; Sepehri-Amin, H.

doi:10.1016/j.scriptamat.2012.06.038

Cited by 600 publications

(218 citation statements)

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“…The -Fe phase content was so small, that its presence was not detected by X-ray studies. The relative content of the superstructures V n of ordinal number n was estimated from the formula: (2) where R n meant surface part of the spectrum attributed to the superstructure, R was the total area of the spectrum, c Fe was the concentration of iron atoms in the sample, c Fe,n was the concentration of iron atoms in superstructure.…”

Section: Resultsmentioning

confidence: 99%

“…of stoichiometric, Re 2 Fe 14 B composition, and with excess of rare earth or iron [1][2][3].Materials, composed of Re-Fe-B compound with overstoichiometric rare earths, typically are characterized by worse glass transition ability, smallest M r /M s ratio and large coercivity. Their properties are shaped by exchange interactions between Re 2 Fe 14 B, which are weakened by an increased distance between the grains.…”

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The microstructure and magnetic properties of Nd_8.5Tb_1.5Fe₈₃Zr₁B₆ ribbons obtained at various cooling rates

et al. 2015

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IntroductionModern Re-Fe-B hard magnetic materials, produced using rapid quenching technique, taking into account variations in chemical composition, can be divided into three groups i.e. of stoichiometric, Re 2 Fe 14 B composition, and with excess of rare earth or iron [1][2][3].Materials, composed of Re-Fe-B compound with overstoichiometric rare earths, typically are characterized by worse glass transition ability, smallest M r /M s ratio and large coercivity. Their properties are shaped by exchange interactions between Re 2 Fe 14 B, which are weakened by an increased distance between the grains. Enlarged distance between grains is resulting from the presence of a thin boundary formed from an amorphous matrix of redundant rare earths. Additionally, the presence of such a boundary causes an increase in coercivity due to the strong bonding of domain walls at the grain boundaries [4]. The stoichiometric composition causes increase in glass transition ability, M r /M s ratio but also causes deterioration of coercivity. These changes are a result of a reduction in the distance between grains, by removing the paramagnetic amorphous matrix, and fi ner structure as a result of increase in glass transition ability [5]. The highest glass transition ability, fi ner structure and highest M r /M s ratio is met in Re-Fe-B compound with overstoichiometric iron. The signifi cantly higher value of the M r /M s ratio results from the presence of the strong exchange interactions, between particles that differ in magnetic hardness. The grains, of soft magnetic phase, have ribbons obtained by melt-spinning technique. The samples were produced using the rapid cooling of liquid alloy on the copper wheel, by applying three different linear velocities 20, 30, and 35 m/s. The microstructure of obtained ribbons was examined using X-ray diffractometry and Mössbauer spectroscopy. Magnetic measurements were performed using LakeShore vibrating sample magnetometer. The microstructure measurements were used for quantitative and qualitative analysis of phase composition. Basing on results of structure studies combined with magnetic measurements, the infl uence of phase composition on hysteresis loop behavior was described.

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Section: Resultsmentioning

confidence: 99%

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The microstructure and magnetic properties of Nd_8.5Tb_1.5Fe₈₃Zr₁B₆ ribbons obtained at various cooling rates

et al. 2015

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“…In recent years, the relationship between the coercivity and the microstructure of sintered magnets, such as the grain size and the composition of the Nd-rich GB phase, has been experimentally clarified. 4,5 To interpret these experimental results, micromagnetic simulations for various model structures have been employed. 6,7 The modeled structures for the simulation must include multiple grains and thin GB layers, because the statistical treatment of the domain wall propagation through the GB layers is necessary to understand the magnetization reversal mechanism of sintered magnets.…”

Section: Introductionmentioning

confidence: 99%

Large-scale micromagnetic simulation of Nd-Fe-B sintered magnets with Dy-rich shell structures

et al. 2016

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Large-scale micromagnetic simulations have been performed using the energy minimization method on a model with structural features similar to those of Dy grain boundary diffusion (GBD)-processed sintered magnets. Coercivity increases as a linear function of the anisotropy field of the Dy-rich shell, which is independent of Dy composition in the core as long as the shell thickness is greater than about 15 nm. This result shows that the Dy contained in the initial sintered magnets prior to the GBD process is not essential for enhancing coercivity. Magnetization reversal patterns indicate that coercivity is strongly influenced by domain wall pinning at the grain boundary. This observation is found to be consistent with the one-dimensional pinning theory.

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“…Therefore, developing high coercivity Nd-Fe-B permanent magnets without HRE elements have drawn a great deal of attention [2]. Actually, the coercivity of the commercial Nd-Fe-B permanent magnets without HRE elements (H ci ∼12 kOe) is considerably lower than that expected from their anisotropic magnetic field (H A ∼73 kOe) [3], which can be attributed to insufficient microstructure control [3,4]. Accordingly, the control of microstructures such as grain size and grain boundary is of significant importance to improve magnetic properties of Nd-Fe-B permanent magnets without HRE elements.…”

Section: Introductionmentioning

confidence: 99%

Effect Of The Desorption-Recombination Temperature On The Microstructure And Magnetic Properties Of HDDR Processed Nd-Fe-B Powders

Lee

Cha

Liu

et al. 2015

Archives of Metallurgy and Materials

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The effect of the desorption-recombination temperature on the microstructure and magnetic properties of hydrogenationdisproportionation-desorption-recombination (HDDR) processed Nd-Fe-B powders was studied. The Nd x B 6.4 Ga 0.3 Nb 0.2 Fe bal (x=12.5-13.5, at.%) casting alloys were pulverized after homogenizing annealing, and then subjected to HDDR treatment. During the HDDR process, desorption-recombination (DR) reaction was induced at two different temperature, 810 • C and 820 • C. The higher Nd content resulted in enhanced coercivity of the HDDR powder, and which was attributed to the thicker and more uniform Nd-rich phase along grain boundaries. But this uniform Nd-rich phase induced faster grain growth. The remanence of the powder DR-treated at 820 • C is higher than that DR-treated at 810 • C. In addition, it was also confirmed that higher DR temperature is much more effective to improve squareness.

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Strategy for high-coercivity Nd–Fe–B magnets

Cited by 600 publications

References 40 publications

The microstructure and magnetic properties of Nd_8.5Tb_1.5Fe₈₃Zr₁B₆ ribbons obtained at various cooling rates

The microstructure and magnetic properties of Nd_8.5Tb_1.5Fe₈₃Zr₁B₆ ribbons obtained at various cooling rates

Large-scale micromagnetic simulation of Nd-Fe-B sintered magnets with Dy-rich shell structures

Effect Of The Desorption-Recombination Temperature On The Microstructure And Magnetic Properties Of HDDR Processed Nd-Fe-B Powders

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Strategy for high-coercivity Nd–Fe–B magnets

Cited by 600 publications

References 40 publications

The microstructure and magnetic properties of Nd8.5Tb1.5Fe83Zr1B6 ribbons obtained at various cooling rates

The microstructure and magnetic properties of Nd8.5Tb1.5Fe83Zr1B6 ribbons obtained at various cooling rates

Large-scale micromagnetic simulation of Nd-Fe-B sintered magnets with Dy-rich shell structures

Effect Of The Desorption-Recombination Temperature On The Microstructure And Magnetic Properties Of HDDR Processed Nd-Fe-B Powders

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The microstructure and magnetic properties of Nd_8.5Tb_1.5Fe₈₃Zr₁B₆ ribbons obtained at various cooling rates

The microstructure and magnetic properties of Nd_8.5Tb_1.5Fe₈₃Zr₁B₆ ribbons obtained at various cooling rates