Experimental and computational analysis of magnetization reversal in (Nd,Dy)-Fe-B core shell sintered magnets

Helbig, Tim; Loewe, Konrad; Sawatzki, Simon; Yi, Min; Xu, Bai‐Xiang; Gutfleisch, Oliver

doi:10.1016/j.actamat.2017.01.055

Cited by 63 publications

(25 citation statements)

References 32 publications

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“…grain shape/size, grain boundary, intergranular phase, etc.) on the magnetization reversal process and the macroscopic properties of permanent magnets [10][11][12][13][14][15][16][17][18][19]. The thermal activation of nucleation at finite temperatures and its effect on the decay of coercive field in Nd-Fe-B magnets are addressed by micromagnetic simulations [20,21], but the temperaturedependent intrinsic properties have to be already known or determined beforehand.…”

Section: Introductionmentioning

confidence: 99%

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Gong

Evans

et al. 2019

Phys. Rev. B

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Temperature-dependent magnetic properties of Nd2Fe14B permanent magnets, i.e., saturation magnetization Ms(T ), effective magnetic anisotropy constants K eff i (T ) (i = 1, 2, 3), domain wall width δw(T ), and exchange stiffness constant Ae(T ), are calculated by using ab-initio informed atomistic spin model simulations. We construct the atomistic spin model Hamiltonian for Nd2Fe14B by using the Heisenberg exchange of Fe−Fe and Fe−Nd atomic pairs, the uniaxial single-ion anisotropy of Fe atoms, and the crystal-field energy of Nd ions which is approximately expanded into an energy formula featured by second, fourth, and sixth-order phenomenological anisotropy constants. After applying a temperature rescaling strategy, we show that the calculated Curie temperature, spin-reorientation phenomenon, Ms(T ), δw(T ), and K eff i (T ) agree well with the experimental results. Ae(T ) is estimated through a general continuum description of the domain wall profile by mapping atomistic magnetic moments to the macroscopic magnetization. Ae is found to decrease more slowly than K eff 1 with increasing temperature, and approximately scale with normalized magnetization as Ae(T ) ∼ m 1.2 . Especially, the possible domain wall configurations at temperatures below the spin-reorientation temperature and the associated δw and Ae are identified. This work provokes a scale bridge between ab-initio calculations and temperature-dependent micromagnetic simulations of Nd-Fe-B permanent magnets.

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Section: Introductionmentioning

confidence: 99%

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Gong

Evans

et al. 2019

Phys. Rev. B

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“…Microstructure engineering has been explored to design high-coercivity Nd-Fe-B magnets, e.g. optimizing the grain shape and reducing the grain size to decrease the local effective demagnetization factor N eff [10][11][12][13][14], doping Nd 2 Fe 14 B grain or its surface with Dy or Tb to increase the anisotropy field H A [15][16][17][18], deceasing M s of GB to make Nd 2 Fe 14 B grains exchange decoupled by GB diffusion [19][20][21], etc. Based on the micromagnetic theory, the coercivity of Nd-Fe-B magnets can be tailored by controlling the distribution of three parameters, i.e.…”

Section: Introductionmentioning

confidence: 99%

Anisotropic exchange in Nd–Fe–B permanent magnets

Gong

Evans

Gutfleisch

et al. 2019

Materials Research Letters

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The exchange is critical for designing high-performance Nd-Fe-B permanent magnets. Here we demonstrate through multiscale simulations that the exchange in Nd-Fe-B magnets, including bulk exchange stiffness (A e) in Nd 2 Fe 14 B phase and interface exchange coupling strength (J int) between Nd 2 Fe 14 B and grain boundary (GB), is strongly anisotropic. A e is larger along crystallographic a/b axis than along c axis. Even when the GB Fe x Nd 1−x has the same composition, J int for (100) interface is much higher than that for (001) interface. The discovered anisotropic exchange is shown to have profound influence on the coercivity. These findings enable more freedom in designing Nd-Fe-B magnets by tuning exchange. IMPACT STATEMENT Bulk exchange stiffness in Nd 2 Fe 14 B and interface exchange coupling strength between Nd 2 Fe 14 B and grain boundary are found strongly anisotropic, which have profound influence on the coercivity of Nd-Fe-B magnets.

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“…Since their discovery in 1980-ies, the Nd-Fe-B-based alloys remain the best ones among other permanent magnets [1][2][3][4][5][6][7]. They possess the highest magnetic energy product (BH c ) max (B being the saturation magnetization, and H c being the coercivity).…”

Section: Introductionmentioning

confidence: 99%

“…However, the coercivity is still far away from its possible maximum. H c increases if the domain walls have a limited mobility, and cannot penetrate through the grain boundary (GB) from one Nd 2 Fe 14 B grain to another when the external magnetic field changes its direction and value [4,5].…”

Section: Introductionmentioning

confidence: 99%

Grain boundaries in Nd-Fe-B-based alloys

et al. 2020

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In this review we consider the microstructure of grain boundaries (GBs) in the Nd-Fe-B-based alloys for permanent magnets. It is generally accepted that the unique hard magnetic properties of such alloys are controlled by the thin layers of a Nd-rich phase in Nd 2 Fe 14 B / Nd 2 Fe 14 B GBs. These GB layers ensure the magnetic isolation of Nd 2 Fe 14 B grains from each other. It is generally supposed that such GB layers contain metallic Nd or Nd-rich intermetallic compounds. However, the commercial Nd-Fe-B-based permanent magnets frequently contain the tangible amount of neodymium oxide Nd 2 O 3 in the triple junctions between Nd 2 Fe 14 B grains. In this review we show that oxide layers are also present in the GBs in Nd-Fe-B-based permanent magnets. The Nd-based phase in GBs can form continous layers between Nd 2 Fe 14 B grains (this case is called complete wetting). It corresponds to the zero contact angle between GB and Nd-rich phase. If the contact angle is non-zero, the Nd-based phase forms the chain of particles in the GB. In turn, if the GB between these particles is "dry", this case is called the incomplete wetting. If the GB between the Nd-rich particles contains the thin layer of a Nd-rich phase (either metallic or oxide), this case is called the pseudo-incomplete (or pseudo-partial) GB wetting.

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Experimental and computational analysis of magnetization reversal in (Nd,Dy)-Fe-B core shell sintered magnets

Cited by 63 publications

References 32 publications

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Calculating temperature-dependent properties of Nd2Fe14B permanent magnets by atomistic spin model simulations

Anisotropic exchange in Nd–Fe–B permanent magnets

Grain boundaries in Nd-Fe-B-based alloys

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