Micromagnetic simulations of magnetization reversals in Nd-Fe-B permanent magnets

H. Sepehri-Amin¹, T. Ohkubo², and K. Hono²

¹International Center for Young Scientists, NIMS, Japan

²Magnetic Materials Unit, NIMS, Japan

Anisotropic Nd-Fe-B sintered magnets are currently known as the highest performance permanent magnets. However, low coercivity is the main drawback when we consider them for high temperature applications such as traction motors of hybrid cars. To improve the coercivity, it is necessary to obtain a better understanding of the weak points for the magnetization reversal process in these magnets.

In this talk, the finite element micromagnetic simulation will be introduced which can simulate the magnetization process of permanent magnets with multi-phase polycrystalline microstructures. The key points for making a realistic geometry of Nd-Fe-B permanent magnets based on microstructure studies will be discussed. We will also address what needs to be considered to solve a dynamic micromagnetic code. Micromagnetic simulation results showed that with reducing the magnetization of the grain boundary phase and enhancing the anisotropy field at the interfaces, coercivity can be enhanced via increasing the nucleation field and changing the nucleation sites for reversed domains. Based on the results, we will discuss how to enhance the coercivity further. Thereafter, a practical application will be shown in which the coercivity of hot deformed Nd-Fe-B magnets was successfully enhanced to a level of 2.6 T by a grain boundary/interface chemistry modification.