Abstract
We performed a large-scale micromagnetics simulation on a supercomputing system to investigate the properties of isotropic nanocrystalline permanent magnets consisting of cubic grains. In the simulation, we solved the Landau–Lifshitz–Gilbert equation under a periodic boundary condition for accurate calculation of the magnetization dynamics inside the nanocrystalline isotropic magnet. We reduced the inter-grain exchange interaction perpendicular and parallel to the external field independently. Propagation of the magnetization reversal process is inhibited by reducing the inter-grain exchange interaction perpendicular to the external field, and the coercivity is enhanced by this restraint. In contrast, when we reduce the inter-grain exchange interaction parallel to the external field, the coercivity decreases because the magnetization reversal process propagates owing to dipole interaction. These behaviors show that the coercivity of an isotropic permanent magnet depends on the direction of the inter-grain exchange interaction.
Highlights
The magnetization dynamics governs the properties of permanent magnets, which are applied in various devices such as the actuators in hard disk drives and high-power motors for electric vehicles.[1,2] A nanocrystalline permanent magnet consists of many grains whose diameters range between nano and submicron scale.[3,4,5,6,7,8] The grains are separated from each other by grain boundary phases
Micromagnetics simulation based on the Landau–Lifshitz–Gilbert (LLG) equation are widely used in magnetic research to investigate the magnetization dynamics because the magnetization reversal process can be observed directly.[9,10,11,12,13]
Micromagnetics simulations have been applied for investigating permanent magnets, it is difficult to simulate the magnetization dynamics inside the magnet accurately
Summary
The magnetization dynamics governs the properties of permanent magnets, which are applied in various devices such as the actuators in hard disk drives and high-power motors for electric vehicles.[1,2] A nanocrystalline permanent magnet consists of many grains whose diameters range between nano and submicron scale.[3,4,5,6,7,8] The grains are separated from each other by grain boundary phases. The magnetization dynamics in nanocrystalline permanent magnets has been investigated for a long time It is still not clear how the magnetization reversal process propagates in a permanent magnet. Micromagnetics simulation based on the Landau–Lifshitz–Gilbert (LLG) equation are widely used in magnetic research to investigate the magnetization dynamics because the magnetization reversal process can be observed directly.[9,10,11,12,13] micromagnetics simulations have been applied for investigating permanent magnets, it is difficult to simulate the magnetization dynamics inside the magnet accurately. We implemented a new type of fast Fourier transform algorithm that enables performing micromagnetics simulation using more than 0.1 billion calculation cells in a super computing system.[14,15,16] we can accurately simulate the propagation of the magnetization reversal process inside the magnet. Reversal process depends on the strength and the direction of the inter-grain exchange interaction
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