Microstructure Origin of the Large Coercivity in an (Nd, Dy)-Fe-B Sintered Magnet

Tomography-based Digital Twin of Nd-Fe-B Permanent Magnets

“…However, the reasonable question arises either it was just a quantitative match, or the tomography-based model could describe the coercivity mechanism of hot-deformed magnets in general. To answer this question, we also performed simulations of the angular dependence of coercivity which is commonly used to reveal the coercivity mechanism [6,22,[40][41][42][43][44].…”

“…4a). Although the ferromagnetic nature of IGP is justified, the actual value of µ0Ms is not well establisheddifferent experimental techniques provided estimations in the range of 0.4 -1.2 T for sintered magnets [6,[36][37][38]. Therefore, we varied the IGP magnetization from 0 to 1.5 T to cover a wide range of possibilities in simulations, while the IGP exchange stiffness was scaled as 𝐴 ∝ 𝑀 𝑠 2 [17,33].…”

“…After the decades of research since the Nd2Fe14B compound was discovered [2,3], the maximum energy product of Nd-Fe-B magnets has almost reached its theoretical limit. However, the coercivity of industrial Nd-Fe-B magnets, which quantifies the resistance of a magnet to demagnetization in opposing magnetic fields, is still only about 20-25% of its potential given by the anisotropy field (μ0Ha ~ 7.5 T) [4][5][6].…”

“…Such a discrepancy, known as the Brown paradox [7], is mainly due to microstructural imperfections and defects that promote the nucleation of reversed magnetic domains at much lower magnetic fields than Ha. In order to achieve a high coercivity, Nd-Fe-B magnets should consist of small Nd2Fe14B grains (D < 1 µm) which are well aligned with c-axes and isolated from each other by a thin nonmagnetic intergranular phase (IGP), or at least by a weakly ferromagnetic one [5,6]. In addition, soft magnetic secondary phases should be eliminated, while grains on the magnet surface should be protected from any damage or strengthened, e.g., by Dy diffusion [8].…”

“…The laborious optimization of Nd-Fe-B magnets towards the desired microstructure and magnetic performance is still in progress [9][10][11][12][13][14][15][16]. To accelerate this process, micromagnetic simulations are often used to elucidate the relationships between microstructural features and macroscopic magnetic properties [6,[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. Current micromagnetic models of Nd-Fe-B magnets address the two cases of high practical importance: sintered magnets [6,8,[20][21][22][23] and hot-deformed ones [24][25][26][27][28][29][30][31][32].…”