Large-scale micromagnetic simulation of Nd-Fe-B sintered magnets with Dy-rich shell structures

Abstract

Large-scale micromagnetic simulations have been performed using the energy minimization method on a model with structural features similar to those of Dy grain boundary diffusion (GBD)-processed sintered magnets. Coercivity increases as a linear function of the anisotropy field of the Dy-rich shell, which is independent of Dy composition in the core as long as the shell thickness is greater than about 15 nm. This result shows that the Dy contained in the initial sintered magnets prior to the GBD process is not essential for enhancing coercivity. Magnetization reversal patterns indicate that coercivity is strongly influenced by domain wall pinning at the grain boundary. This observation is found to be consistent with the one-dimensional pinning theory.

Preconditioned nonlinear conjugate gradient method for micromagnetic energy minimization

“…Micromagnetic models which are used for the analysis and design of permanent magnets are huge. Typically the number of finite elements exceeds 20 million elements [41,32]. As a consequence fast solvers for computing the demagnetization curve are required.…”

Magnetic microstructure machine learning analysis

“…The grains with higher anisotropy field have a composition (Nd 1−x Dy x ) 2 Fe 14 B. Following Oikawa et al [44] we decrease the spontaneous magnetization M s linearly with increasing Dy-content. For the grains with higher anisotropy field we used (Nd 0.9 Dy 0.1 ) 2 Fe 14 B or (Nd 0.66 Dy 0.34 ) 2 Fe 14 B with a magnetization μ 0 M s =1.52 T and 1.3T, respectively.…”

Rationally selecting the chemical composition of the Nd–Fe–B magnet for high-efficiency grain boundary diffusion of heavy rare earths

“…This indicates that the over-high concentration of HRE in the HRE-rich shells is unnecessary but causes an unexpected waste of HRE resources. In addition, a large-scale micromagnetic simulation by Oikawa et al 38 revealed that a 15 nm-thick Dy-rich shell is sufficient for coercivity enhancement. Therefore, for highly efficient use of the HRE sources, a deep diffusion depth of HRE and thin HRE-rich shell should be achieved by GBD.…”