Abstract
We numerically demonstrated the magnetization reversal process inside a hot-deformed nanocrystalline permanent magnet. We performed large-scale micromagnetics simulation based on the Landau–Lifshitz–Gilbert equation with 0.1 billion calculation cells. The simulation model for the hot-deformed nanocrystalline permanent magnet consists of 2622 tabular grains that interact with each other by inter-grain exchange and dipole interactions. When the strength of the external field approached a coercive force, nucleation cores were created at the grain surface. The magnetization reversal was propagated by the inter-grain and dipole interactions. When the grains had overlapping regions parallel to the external field, the magnetization reversal propagated quickly between the grains due to the dipole interaction. In contrast, the motion of the magnetic domain wall was inhibited at interfaces between the grains perpendicular to the external field. Reversal magnetic domains had a pillar-shaped structure that is parallel to the external field. In the perpendicular direction, the reversal magnetic domain expanded gradually because of the inhibition of the domain wall motion.
Highlights
Nd–Fe–B hot-deformed nanocrystalline permanent magnet is one of the most attractive permanent magnet.[1,2,3,4] The magnet consists of many tabular grains with diameters at the sub-micron scale and easy axes are oriented to almost the same direction
We demonstrated the propagation of magnetization reversal in Nd–Fe–B nanocrystalline hotdeformed permanent magnets through a large-scale micromagnetics simulation using 0.1 billion calculation cells
The model of the nanocrystalline permanent magnet consisted of 2622 tabular grains with a diameter of about 127 nm and thickness 32 nm
Summary
Nd–Fe–B hot-deformed nanocrystalline permanent magnet is one of the most attractive permanent magnet.[1,2,3,4] The magnet consists of many tabular grains with diameters at the sub-micron scale and easy axes are oriented to almost the same direction. To realize a high performance of the nanocrystalline permanent magnet, it is important to understand a propagation of a magnetization reversal in the gains and across grain boundaries. In many previous works, the micromagnetics simulations were performed under open boundary condition. Even if the side length of the simulation model reaches micro-meter, magnetization dynamics is simulated only on surface of the permanent magnets.[8] the number of the grains is small to investigate magnetic domain structure in real permanent magnets.[9,10,11,12]. Enables micromagnetics simulation using 0.1 billion calculation cells.[13,14,15] We demonstrate magnetization reversal and stabilized magnetization structure in simulation model which has over 1,000 grains
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