Magnetization reversal of exchange-coupled and exchange-decoupled Nd-Fe-B magnets observed by magneto-optical Kerr effect microscopy

Soderžnik, Marko; Sepehri-Amin, H.; Sasaki, Taisuke; Ohkubo, T.; Takada, Yoko; Sato, T.; Kaneko, Yuji; Kato, Akira; Schrefl, T.; Hono, K.

doi:10.1016/j.actamat.2017.05.006

Cited by 118 publications

(26 citation statements)

References 28 publications

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“…Magnetic nucleation and domain wall motion reduce the coercivity. When the external magnetic field approaches the coercivity, the magnetization starts to be reversed in tabular grains, and the domain walls move into the other grains [11][12][13][14][15] . Although the origins of magnetization reversal have been theoretically and experimentally investigated, it remains to be clarified how magnetization reversal is nucleated inside a permanent magnet [16][17][18][19] .…”

Section: Introductionmentioning

confidence: 99%

Relationship between magnetic nucleation and the microstructure of a hot-deformed permanent magnet: micromagnetic simulation

et al. 2020

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The grains initiating magnetization reversal in the microstructure of a hot-deformed permanent magnet have been identified in this study by performing micromagnetic simulations based on the Landau-Lifshitz-Gilbert equation. Hotdeformed permanent magnets comprise tabular grains, the easy-axis orientations of which are inclined with respect to the nominal easy axis of the permanent magnet. In the simulation model, the grains complexly overlap, similar to in actual permanent magnets. We analyze the simulation results considering grain overlap and the easy-axis tilt angles of the grains. The initiation of magnetic nucleation requires a high concentration of grains with large easy-axis tilt angles. We clarify the magnetic-nucleation process and provide a method to enhance the performance of permanent magnets by avoiding a high concentration of grains with large easy-axis tilt angles.

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Section: Introductionmentioning

confidence: 99%

Relationship between magnetic nucleation and the microstructure of a hot-deformed permanent magnet: micromagnetic simulation

et al. 2020

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“…Micromagnetic simulations have become an essential tool for the design of soft magnetic sensors [6] and permanent magnets [5,43]. Fast computation of the demagnetization curve is a prerequisite for parameter studies which are applied to find optimal designs [28].…”

Section: Introductionmentioning

confidence: 99%

Preconditioned nonlinear conjugate gradient method for micromagnetic energy minimization

Exl

Fischbacher

Kovacs

et al. 2019

Computer Physics Communications

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Fast computation of demagnetization curves is essential for the computational design of soft magnetic sensors or permanent magnet materials. We show that a sparse preconditioner for a nonlinear conjugate gradient energy minimizer can lead to a speed up by a factor of 3 and 7 for computing hysteresis in soft magnetic and hard magnetic materials, respectively. As a preconditioner an approximation of the Hessian of the Lagrangian is used, which only takes local field terms into account. Preconditioning requires a few additional sparse matrix vector multiplications per iteration of the nonlinear conjugate gradient method, which is used for minimizing the energy for a given external field. The time to solution for computing the demagnetization curve scales almost linearly with problem size.

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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%

“…The experimental determination of M s and K 1 is much easier [25][26][27][28]. Even though the decrease of GB M s to improve coercivity is qualitatively explained by the exchange decoupling [19][20][21], the underlying quantitative interface exchange behavior still remains to be explored.…”

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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Magnetization reversal of exchange-coupled and exchange-decoupled Nd-Fe-B magnets observed by magneto-optical Kerr effect microscopy

Cited by 118 publications

References 28 publications

Relationship between magnetic nucleation and the microstructure of a hot-deformed permanent magnet: micromagnetic simulation

Relationship between magnetic nucleation and the microstructure of a hot-deformed permanent magnet: micromagnetic simulation

Preconditioned nonlinear conjugate gradient method for micromagnetic energy minimization

Anisotropic exchange in Nd–Fe–B permanent magnets

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