Jun Fujisaki

Micromagnetic Simulations of Magnetization Reversal in Misaligned Multigrain Magnets With Various Grain Boundary Properties Using Large-Scale Parallel Computing

This paper reports on micromagnetic simulations of the magnetization reversal behavior in polycrystalline Nd-Fe-B sintered magnets using large-scale parallel computing. A multigrain model is introduced to calculate the grain alignment dependence of the coercivity of polycrystalline Nd-Fe-B magnets with various magnetic characteristics at grain boundaries (GBs). The magnetic domain wall motion is accurately treated by dividing the analyzed object into extremely small elements. The multigrain model with a soft magnetic GB phase and a reverse domain at the initial state well reproduces experimental results. The calculations of coercivity with several GB widths are also carried out to seek for the origin of the sudden decrease of coercivity with nearly perfect grain alignment.

Micromagnetic simulation of the orientation dependence of grain boundary properties on the coercivity of Nd-Fe-B sintered magnets

This paper is focused on the micromagnetic simulation study about the orientation dependence of grain boundary properties on the coercivity of polycrystalline Nd-Fe-B sintered magnets. A multigrain object with a large number of meshes is introduced to analyze such anisotropic grain boundaries and the simulation is performed by combining the finite element method and the parallel computing. When the grain boundary phase parallel to the c-plane is less ferromagnetic the process of the magnetization reversal changes and the coercivity of the multigrain object increases. The simulations with various magnetic properties of the grain boundary phases are executed to search for the way to enhance the coercivity of polycrystalline Nd-Fe-B sintered magnets.

Micromagnetic Hysteresis Model Dealing With Magnetization Flip Motion for Grain-Oriented Silicon Steel

This paper presents a vector hysteresis model based on micromagnetic theory. In this model, a magnetization state of a magnetic material is described by a collection of single-domain particles, and magnetic reversal processes due to domain-wall motions are treated approximately as a magnetization flip. The present model is applied to calculation of hysteresis properties of grain-oriented silicon steel. The simulation results show that the anisotropic hysteresis properties and iron loss can be reproduced accurately by the present model.

Semi-Implicit Steepest Descent Method for Energy Minimization and Its Application to Micromagnetic Simulation of Permanent Magnets

To reveal the relationship between coercivity of permanent magnets and their microstructure, micromagnetics is one of the key technologies for analyzing the magnetization reversal mechanism. Especially, microscopic reversal process such as nucleation of a reversed domain and domain wall pinning has been investigated by micromagnetic simulation [1]. However, since the mesh size in the simulation should be less than the exchange length of a magnet to calculate the domain wall structure accurately, the overall dimensions of models for such simulation is practically limited to very small length scales. Therefore, further improvement in calculation speed are demanded to simulate reversal process of more realistic microstructure.

Loss Simulation by Finite-Element Magnetic Field Analysis Considering Dielectric Effect and Magnetic Hysteresis in EI-Shaped Mn-Zn Ferrite Core

Power electronic devices such as inductors and transformers are required to be driven with high frequency according to downsizing. Mn-Zn ferrite is one of the high-frequency magnetic materials. The dimensional resonance occurs in Mn-Zn cores due to the increase of the dielectric constant and significantly affects the eddy current loss [1]. The equivalent RC circuit of Mn-Zn ferrite was modeled by the grains and their boundary layers and can explain the effective dielectric property by the contribution of the capacitance [2]. The boundary layers with high-resistance suppress the eddy current in the grains at low frequencies, while as frequency increases the suppression of the eddy current decreases by charge accumulation on the surface of the grains. The calculating method of the frequency dependent dielectric property by the capacitance was proposed and the dimensional resonance was reproduced by applying the method to the magnetic field equations of linear magnetic materials by using a cylindrical approximation [3]. In order to analyze the eddy current loss of complex shaped inductors at high frequencies, we apply the dielectric effect to the A-

Magnetic Field Analysis for Dimensional Resonance in Mn–Zn Ferrite Toroidal Core and Comparison With Permeability Measurement

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Speeding Up Micromagnetic Simulation by Energy Minimization With Interpolation of Magnetostatic Field

method of the finite element magnetic field analysis. On the other hand, the magnetic hysteresis loss increases according to the increase of the magnetic flux density in the core. Therefore, we used the play model [4] to express the magnetic hysteresis for finite amplitude of magnetic flux. For confirming the calculation accuracy, core losses of an EI-shaped inductor was calculated and the frequency dependent loss was compared with experimental results. In the simulation, the core loss was divided into hysteresis loss in DC, eddy current loss and excess loss, and their contributions were analyzed. II. METHOD The current density of the grains is

Speeding up micromagnetic simulation by energy minimization with interpolation of magnetostatic field

j_{1}

Experimental and Simulation Modeling Studies of Magnetic Properties of Ni-Zn Ferrite Cores under DC Bias

as follows [3].

Micromagnetic Simulations of Emission Power in Spin Torque Oscillator: Influence of Diameter and Interlayer Exchange Coupling

j_{1} = \sigma_{1}( {E-rq/}\varepsilon )