First principles study on the local magnetic anisotropy near surfaces of Dy2Fe14B and Nd2Fe14B magnets

Tanaka, Susumu; Moriya, Hideshige; Tsuchiura, Hiroki; Sakuma, Atsushi; Diviš, M.; Novák, P.

doi:10.1063/1.3553935

Cited by 36 publications

(14 citation statements)

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“…plane type [99][100][101], in contrast to the easy-axis type in the bulk. On the other hand, surface easyaxis anisotropy may be enhanced by the substitution of strongly anisotropic atoms, e.g., Dy [7,102].…”

Section: Effect Of Surface Propertiesmentioning

confidence: 99%

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Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet

Miyashita

Nishino

Toga

et al. 2021

Science and Technology of Advanced Materials

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For the practical use of magnets, particularly at high temperatures, the temperature dependence of magnetic properties is an important ingredient. To study the temperature dependence, methods of treating the thermal fluctuation causing the so-called activation phenomena must be established. To study finite-temperature properties quantitatively, we need atomistic energy information to calculate the canonical distribution. In the present review, we report our recent studies on the thermal properties of the Nd 2 Fe 14 B magnet and the methods of studying them. We first propose an atomistic Hamiltonian and show various thermodynamic properties, e.g., the temperature dependences of the magnetization showing a spin reorientation transition, the magnetic anisotropy energy, the domain wall profiles, the anisotropy of the exchange stiffness constant, and the spectrum of ferromagnetic resonance. The effects of the dipole-dipole interaction (DDI) in large grains are also presented. In addition to these equilibrium properties, we also study coercivity, which is the most important issue for magnets. The temperature dependence of the coercivity of a single grain was studied using the stochastic Landau-Lifshitz-Gilbert equation and also by the analysis of the free energy landscape, which was obtained by Monte Carlo simulation. It was found that the upper limit of coercivity at room temperature is about 3T, which is significantly lower than the so-called theoretical coercivity given by a simple coherent rotation model. The coercivity of a polycrystalline magnet, i.e., an ensemble of grains, is expected to be reduced further by the effects of the grain boundary phase, which is also studied. Surface nucleation is a key ingredient in the domain wall depinning process. Finally, we study the effect of DDI among grains and also discuss the distribution of properties of grains from the viewpoint of first order reversal curve.

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Section: Effect Of Surface Propertiesmentioning

confidence: 99%

“…is negative and the amplitude is of the same order as that in the bulk[99][100][101], and (3) doubly reinforced anisotropy in Nd atoms:…”

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confidence: 99%

Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet

Miyashita

Nishino

Toga

et al. 2021

Science and Technology of Advanced Materials

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“…In the present work, we perform a combined firstprinciples and micromagnetic study on Nd-Fe-B magnets, in order to demonstrate a multiscale simulation framework for elucidating the strain effects on Nd-Fe-B magnets and to clarify what kind of local strain can significantly reduce the coercivity. Previous first-principles calculations have provided insights into the magnetic moments and the magnetocrystalline anisotropy based on either the crystal field of Nd ions [22][23][24][25][26][27] or the total energy difference [28,29]. Especially, Suzuki et al [23] explored the crystal field parameter of Nd ions in the case of changing the length of a-axes and c-axis.…”

Section: Introductionmentioning

confidence: 99%

Multiscale Examination of Strain Effects in Nd-Fe-B Permanent Magnets

Zhang

Gutfleisch

2017

Phys. Rev. Applied

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We have performed a combined first-principles and micromagnetic study on the strain effects in Nd-Fe-B permanent magnets. First-principles calculations on Nd2Fe14B reveal that the magnetocrystalline anisotropy (K) is insensitive to the deformation along c axis and the ab in-plane shrinkage is responsible for the K reduction. The predicted K is more sensitive to the lattice deformation than what the previous phenomenological model suggests. The biaxial and triaxial stress states have a greater impact on K. Negative K occurs in a much wider strain range in the ab biaxial stress state. Micromagnetic simulations of Nd-Fe-B magnets using first-principles results show that a 3 − 4% local strain in a 2-nm-wide region near the interface around the grain boundaries and triple junctions leads to a negative local K and thus remarkably decreases the coercivity by ∼ 60% or 3 − 4 T. The local ab biaxial stress state is more likely to induce a large loss of coercivity. In addition to the local stress states and strain levels themselves, the shape of the interfaces and the intergranular phases also makes a difference. Smoothing the edge and reducing the sharp angle of the triple regions in Nd-Fe-B magnets would be favorable for a coercivity enhancement.

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“…Nd Dy Fe B 永久磁石の保磁力機構 Fe 14 B における Nd イオンの結晶場パラメーター A 0 2 〈r 2 〉[K］ここで R は Nd または Dy を表す(11)(12) .…”

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Coercivity Mechanism of Nd-Fe-B Magnets: Theoretical Approach Based on First-principles Calculations and Micromagnetic Simulations

宏紀¹,

千春²,

昭正³

2011

Materia Japan

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First principles study on the local magnetic anisotropy near surfaces of Dy2Fe14B and Nd2Fe14B magnets

Cited by 36 publications

References 10 publications

Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet

Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet

Multiscale Examination of Strain Effects in Nd-Fe-B Permanent Magnets

Coercivity Mechanism of Nd-Fe-B Magnets: Theoretical Approach Based on First-principles Calculations and Micromagnetic Simulations

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First principles study on the local magnetic anisotropy near surfaces of Dy2Fe14B and Nd2Fe14B magnets

Cited by 36 publications

References 10 publications

Atomistic theory of thermally activated magnetization processes in Nd2Fe14B permanent magnet

Atomistic theory of thermally activated magnetization processes in Nd2Fe14B permanent magnet

Multiscale Examination of Strain Effects in Nd-Fe-B Permanent Magnets

Coercivity Mechanism of Nd-Fe-B Magnets: Theoretical Approach Based on First-principles Calculations and Micromagnetic Simulations

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Product

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Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet

Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet