Most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets

Abstract

Physically, the coercivity of permanent magnets should scale with the anisotropy field of ferromagnetic compounds, H A ; however, the typical coercivity values of commercial polycrystalline sintered magnets are only ~0.2H A , which is known as Brown's paradox. Recent advances in multi-scale microstructure characterizations using focused ion beam scanning electron microscope (FIB/SEM), aberration corrected scanning transmission electron microscopy (C s -corrected STEM), and atom probe tomography (APT) revealed detailed microstructural features of commercial and experimental Nd-Fe-B magnets. These investigations suggest the magnetism of a thin layer formed along grain boundaries (intergranular phase) is a critical factor that influence the coercivity of polycrystalline magnets. To determine the magnetism of the thin intergranular phase, soft X-ray magnetic circular dichroism (XMCD) and electron holography played critical role. Large scale micromagnetic simulations using the models that are close to real microstructure incorporating the recent microstructure characterization results gave insights on how the coercivity and its thermal stability is influenced by the microstructures.Based on these new findings, coercivity of Nd-Fe-B magnets are being improved to its limit. This review replies to most frequently asked questions about the coercivity of Nd-Fe-B permanent magnets based on our recent studies.

Accelerated discovery of cost-effective Nd–Fe–B magnets through adaptive learning

“…This distinct difference in the microstructure of the Ce-oriented and La-oriented systems is believed to be responsible for the higher H cj of the former. 78 In contrast to La and Ce, Y was rarely recommended by the model, except in 3: C3 (Ce 5 Y 0.5 Co 1 ), where only ∼0.5 wt% Y was included. Although Y was known to improve the temperature stability of Nd 2 Fe 14 B, the observed improvement was found to be insufficient to justify its presence.…”

Influence of silver nanoparticle additivation on Nd-Fe-B permanent magnets produced by Laser Powder Bed Fusion

“…[1,3] Since their development in 1984 [4] , scientists and corporations have been exploring methods to either enhance the magnetic properties of Nd-Fe-B magnets to maximize the utilization of RE materials or to develop techniques to minimize the quantity of RE required without compromising the mechanical and functional properties of the magnets. [5][6][7] Since the RE crisis in 2011, it has been emphasized that the growing demand and the current supply situation generate delivery shortages and possibly sharp price fluctuations. [1,2,7] For rapidly solidified Nd-Fe-B permanent magnet materials, the ternary 2-14-1 phase is the primary component responsible for its overall good magnetic properties [8] .…”

“…[5][6][7] Since the RE crisis in 2011, it has been emphasized that the growing demand and the current supply situation generate delivery shortages and possibly sharp price fluctuations. [1,2,7] For rapidly solidified Nd-Fe-B permanent magnet materials, the ternary 2-14-1 phase is the primary component responsible for its overall good magnetic properties [8] .…”

Simultaneous enhancement of coercivity and saturation magnetization in high-performance anisotropic NdFeB thick films with a Dy diffusion layer

“…15 Therefore, the grain boundary diffusion process (GBDP) is the preferred method to produce NdFeB magnets with a high coercivity and a significantly low HRE content. [15][16][17][18] On this basis, several alloys such as (Dy/Pr)-Cu, (Dy/Tb)-Ga, (Dy/Tb)-Al, Dy-Zn, and DyF 3 were investigated to promote the diffusion of HRE elements. [19][20][21][22][23][24] At the diffusion temperature, the low melting point RE-rich intergranular phase in Nd-Fe-B magnets is in the liquid state.…”