Exchange-stiffness constant of a Nd-Fe-B based nanocomposite determined by magnetic neutron scattering

Bick, Jens-Peter; Suzuki, Kiyonori; Gilbert, Elliot P.; Forgan, E. M.; Schweins, Ralf; Lindner, Peter; Kübel, Christian; Michels, Andreas

doi:10.1063/1.4821453

Cited by 20 publications

(20 citation statements)

References 30 publications

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“…Therefore, many researchers in both experimental and theoretical have studied the thermal properties of K u [13][14][15][16][17][18]. However, regarding A for Nd 2 Fe 14 B, experimentally, the values are observed only at several temperatures [19][20][21][22], and also there is no theoretical estimation of the temperature dependence as far as we know.…”

Section: Introductionmentioning

confidence: 99%

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnetNd2Fe14B

Toga¹,

Nishino²,

Miyashita³

et al. 2018

Phys. Rev. B

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We examine the anisotropic properties of the exchange stiffness constant, A, for rare-earth permanent magnet, Nd2Fe14B, by connecting analyses with two different scales of length, i.e., Monte Carlo (MC) method with an atomistic spin model and Landau-Lifshitz-Gilbert (LLG) equation with a continuous magnetic model. The atomistic MC simulations are performed on the spin model of Nd2Fe14B constructed from ab-initio calculations, and the LLG micromagnetics simulations are performed with the parameters obtained by the MC simulations. We clarify that the amplitude and the thermal property of A depend on the orientation in the crystal, which are attributed to the layered structure of Nd atoms and weak exchange couplings between Nd and Fe atoms. We also confirm that the anisotropy of A significantly affects the threshold field for the magnetization reversal (coercivity) given by the depinning process.

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Section: Introductionmentioning

confidence: 99%

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnetNd2Fe14B

Toga¹,

Nishino²,

Miyashita³

et al. 2018

Phys. Rev. B

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“…Recently, however, several SANS studies on the magnetization reversal of nanocrystalline, nanocomposite, and hot-deformed Nd-Fe-B magnets have been published by some of the authors of the present study as well as another group. [8][9][10][11] Micromagnetic simulations, correlation length analysis, and structural-model analyses developed for soft materials were used in these studies, but analysis methodologies for SANS experiments of permanent magnets have not been well established thus far. Our previous study on a)…”

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confidence: 99%

Magnetization reversal of a Nd-Cu-infiltrated Nd-Fe-B nanocrystalline magnet observed with small-angle neutron scattering

Saito

Ueno

Yano

et al. 2015

Journal of Applied Physics

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The magnetization reversal process of Nd-Fe-B nanocrystalline magnets infiltrated with Nd-Cu alloy was examined using small-angle neutron scattering (SANS). The magnetic-field dependence of SANS intensity revealed a qualitative difference between Nd-Cu-infiltrated samples and as-deformed samples. Insufficient magnetic isolation along the direction perpendicular to the nominal c-axis is expected from comparable SANS intensities for different ranges of q values along this direction. For small q values near the coercivity field, Nd-Cu-infiltrated samples show a noticeable reduction in SANS intensity along the nominal c-axis, which is parallel to the external magnetic field. This indicates less spatial fluctuation of magnetic moments in Nd-Cu-infiltrated samples, owing to magnetically isolated Nd2Fe14B grains.

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“…[14] for a review) provides information about the variations of both the magnitude and orientation of the magnetization vector field in the bulk and on a nanometer length scale (approximately 1-300 nm). SANS is extremely sensitive to longwavelength magnetization fluctuations, and it has only recently been employed for characterizing Nd-Fe-B-based permanent magnets: for example, the field dependence of characteristic magnetic length scales during the magnetization-reversal process in isotropic Nd-Fe-B-based nanocomposites [15] and in isotropic sintered Nd-Fe-B [16] was studied, the exchange-stiffness constant has been determined [17], the observation of the so-called spike anisotropy in the magnetic SANS cross section has been explained with the formation of flux-closure patterns [18], magnetic multiple scattering has been detected [19], textured Nd-Fe-B has been investigated [20], and the effect of grain-boundary diffusion on the magnetization-reversal process of isotropic [21] and hot-deformed textured [22][23][24] nanocrystalline Nd-Fe-B magnets has been studied. In this paper, exchange-coupled model magnets are investigated by SANS in order to quantitatively evaluate the spin disorder and to clarify the possible anisotropy of magnetic interactions.…”

Section: Introductionmentioning

confidence: 99%

Spin Structures of Textured and Isotropic Nd-Fe-B-Based Nanocomposites: Evidence for Correlated Crystallographic and Spin Textures

et al. 2017

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We report the results of a comparative study of the magnetic microstructure of textured and isotropic Nd 2 Fe 14 B=α-Fe nanocomposites using magnetometry, transmission electron microscopy, synchrotron x-ray diffraction, and, in particular, magnetic small-angle neutron scattering (SANS). Analysis of the magnetic neutron data of the textured specimen and computation of the correlation function of the spinmisalignment SANS cross section suggests the existence of inhomogeneously magnetized regions on an intraparticle nanometer length scale, about 40-50 nm in the remanent state. Possible origins for this spin disorder are discussed: it may originate in thin-grain-boundary layers (where the material parameters are different than in the Nd 2 Fe 14 B grains), or it may reflect the presence of crystal defects (introduced via hot pressing), or the dispersion in the orientation distribution of the magnetocrystalline anisotropy axes of the Nd 2 Fe 14 B grains. X-ray powder diffraction data reveal a crystallographic texture in the direction perpendicular to the pressing direction-a finding which might be related to the presence of a texture in the magnetization distribution, as inferred from the magnetic SANS data.

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Exchange-stiffness constant of a Nd-Fe-B based nanocomposite determined by magnetic neutron scattering

Cited by 20 publications

References 30 publications

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnetNd2Fe14B

Anisotropy of exchange stiffness based on atomic-scale magnetic properties in the rare-earth permanent magnetNd2Fe14B

Magnetization reversal of a Nd-Cu-infiltrated Nd-Fe-B nanocrystalline magnet observed with small-angle neutron scattering

Spin Structures of Textured and Isotropic Nd-Fe-B-Based Nanocomposites: Evidence for Correlated Crystallographic and Spin Textures

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