Magnetic anisotropy of the Nd2Fe14B compound and its hydride Nd2Fe14BH4

Mushnikov, N. V.; Терентьев, П. Б.; Rosenfeld, E. V.

doi:10.1134/s0031918x0701005x

Cited by 20 publications

(9 citation statements)

References 31 publications

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“…[43]. Employing these parameters, we showed the SR transition with transition temperature T R = 150 K, which is close to experimentally estimated ones [8][9][10]35], and the critical temperature T c ∼ 850 K [22,23], which is a little overestimated to the experimental values T c ∼ 600 K [5,8].…”

Section: Model and Methods A Atomistic Hamiltonian For Nd2fe14bsupporting

confidence: 81%

“…The realization of stronger coercivity at higher temperatures is a central issue in the development of permanent magnet materials for higher efficiency in energy conversion devices such as electric motors, generators, and electronic devices [1]. The Nd magnet, Nd 2 Fe 14 B, is a very important target magnet because of its high coercive force [2][3][4][5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

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Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

2021

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The Nd permanent magnet (Nd2Fe14B) is an indispensable material used in modern energy conversion devices. The realization of high coercivity at finite temperatures is a burning issue. One of the important ingredients for controlling the coercive force is the surface property of magnetic grains. It has been reported by first-principles studies that the Nd atoms in the first (001) surface layer facing the vacuum have in-plane anisotropy perpendicular to the c axis, which may decrease the coercivity. Focusing on the surface anisotropy effect on the coercivity, we examine the coercivity at zero and finite temperatures by using an atomistic model reflecting the lattice structure of the Nd magnet with a stochastic Landau-Lifshitz-Gilbert equation method. We study general three cases, in which the Nd atoms in surface layers have (1) no anisotropy, (2) in-plane anisotropy, and (3) reinforced anisotropy for two types of surfaces, ( 001) and ( 100) surfaces. We find that in contrast to the zero-temperature case, due to the thermal fluctuation effect, the modification of only the first surface layer has little effect on the coercivity at finite temperatures. However, the modification of a few layers results in significant effects. We discuss the details of the dependence of the coercivity on temperature, type of surface, and modified layer depth, and also the features of domain growth in magnetization reversal.

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Section: Model and Methods A Atomistic Hamiltonian For Nd2fe14bsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

2021

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“…exhibits a spin-reorientation (SR) transition at r T 135K, below which the magnetization is tilted from the c-axis [7][8][9]63]. For the tilt in the ground state, the anisotropy energy must have the minimum point at a non-zero angle from the c-axis.…”

Section: Magnetizationsmentioning

confidence: 99%

“…The neodymium (Nd) polycrystalline magnet consisting of Nd 2 Fe 14 B [1][2][3][4][5][6][7][8][9][10][11][12][13][14] is an important high-performance permanent magnet. Because of its high coercivity, it is widely used for electric motors, electronic devices, and so forth.…”

Section: Introductionmentioning

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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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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“…Therefore including the exchange in the total energy density expression would not affect either a minimization process to calculate M(H), [3,4,14,[35][36][37][38][39] or magnetization calculated within the framework of the present work, because calculation of the isothermal magnetization curves from the partition function is done on the magnetization angular coordinates, the exchange interaction is independent of such coordinates. Using this energy expression is not infrequent in the literature, e.g., references [40]- [49] used it for systems with collinear sublattice magnetization [37] for R 2 Fe 14 B system.…”

Section: Theoretical Model and Computationmentioning

confidence: 99%

Diverse features of magnetization curves of uniaxial crystals: A simulation study

Sobh¹,

Aly²

2017

Chinese Phys. B

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We present a simulation of the magnetization curves, energy, probability, and torque landscapes of uniaxial systems with up to five anisotropy constants. The total energy used in the simulation is the sum of the anisotropy and Zeeman energies. The exchange interaction is not considered in the present work in which we treat single-domain-particle systems within a classical mechanics-based model. Diverse features of the calculated magnetization curves are highlighted for the studied systems. These diverse features are strongly dependent on the sign and magnitude of the simulation parameters. The model is versatile enough to handle both hypothetical and real material systems, e.g. HoFe 11 Ti and Y 2 Co 17 .

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Magnetic anisotropy of the Nd2Fe14B compound and its hydride Nd2Fe14BH4

Cited by 20 publications

References 31 publications

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet

Diverse features of magnetization curves of uniaxial crystals: A simulation study

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Magnetic anisotropy of the Nd2Fe14B compound and its hydride Nd2Fe14BH4

Cited by 20 publications

References 31 publications

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

Atomistic theory of thermally activated magnetization processes in Nd2Fe14B permanent magnet

Diverse features of magnetization curves of uniaxial crystals: A simulation study

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Product

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Atomistic theory of thermally activated magnetization processes in Nd₂Fe₁₄B permanent magnet