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.

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Size dependence of the thermal stability factor (Δ) for perpendicular CoFeB/MgO-based magnetic tunnel junctions (p-MTJs) was investigated using the string method in the framework of finite element micromagnetics. The simulation revealed that Δ showed significant size dependence, and the reversal mode changed from coherent rotation to domain wall (DW) motion as MTJ size increased. It also elucidated that Δ depended on the exchange stiffness constant in DW mediated reversal region. These Δ simulations can reproduce the experimental data and can be helpful for MTJ device design.

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