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

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. Hot-deformed 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. Simulations by researchers in Japan have established a better understanding of magnetic switching in permanent magnets. Although devices relying on magnetism such as electrical motors and magnetic memories have long been used, their performance can still be improved with better control of magnetic behavior such as the switching of the magnetic field direction. Hiroshi Tsukahara from the High Energy Accelerator Research Organization in Tsukuba and colleagues have used simulations to study the relationship between this magnetization reversal and the microstructure of a magnet. In the so-called hot-deformed permanent magnets studied by the group, this microstructure consists of packed tabular magnetic regions called grains. The researchers showed that the performance of permanent magnets can be enhanced by avoiding a high concentration of grains with the wrong magnetic alignment. Initiations of magnetic reversals can be described by microstructures of the hot-deformed permanent magnet. Strong dipole fields are applied at magnetic-nucleation sites. Inclinations of easy axes from a nominal easy axis are essential to generate the magnetic nucleation. The magnetization reversal tends to starts from regions in which the grains having tilted easy axis are concentrated. The results of this study show that the performance of the hot-deformed permanent magnet is enhanced by avoiding the concentration of the grains with the tilted easy axis.