Anisotropic exchange in Nd–Fe–B permanent magnets

Abstract

The exchange is critical for designing high-performance Nd-Fe-B permanent magnets. Here we demonstrate through multiscale simulations that the exchange in Nd-Fe-B magnets, including bulk exchange stiffness (A e) in Nd 2 Fe 14 B phase and interface exchange coupling strength (J int) between Nd 2 Fe 14 B and grain boundary (GB), is strongly anisotropic. A e is larger along crystallographic a/b axis than along c axis. Even when the GB Fe x Nd 1−x has the same composition, J int for (100) interface is much higher than that for (001) interface. The discovered anisotropic exchange is shown to have profound influence on the coercivity. These findings enable more freedom in designing Nd-Fe-B magnets by tuning exchange. IMPACT STATEMENT Bulk exchange stiffness in Nd 2 Fe 14 B and interface exchange coupling strength between Nd 2 Fe 14 B and grain boundary are found strongly anisotropic, which have profound influence on the coercivity of Nd-Fe-B magnets.

Atomistic theory of thermally activated magnetization processes in Nd2Fe14B permanent magnet

“…These results well reproduce the experimental data, and thus we confirmed the validity of the model. Similar works with an atomistic model for the finite-temperature properties of magnetization and the domain wall have been recently reported by Gong and coauthors [26][27][28], who obtained thermodynamic quantities and also an effective continuous model. Using the model, they obtained the dependence of stiffness constants on the direction and the coercivity of a system with a grain boundary phase as mentioned above [24].…”

“…The thus obtained temperature dependence of the stiffness constants along the a-axis ( ) and c-axis ( ) is depicted in Figure 7(b ). Gong et al have obtained a similar direction dependence of the stiffness constants and extended the study to the interface exchange coupling strength between the Nd magnet and the grain boundary phase [ 28 ].…”

“…To obtain the stiffness constants at a given temperature, we used domain wall energy obtained a similar direction dependence of the stiffness constants and extended the study to the interface exchange coupling strength between the Nd magnet and the grain boundary phase [28].…”

Effect of the surface magnetic anisotropy of neodymium atoms on the coercivity in neodymium permanent magnets

“…Micromagnetics continuum modellings for permanent magnets have been applied in analyses of magnetic properties of the Nd magnet [21]. However, to study the microscopic details, recently developed atomistic models are indispensable [16,[22][23][24][25][26][27][28][29][30][31][32][33][34]. Unlike the continuum modellings, the lattice structure (Fig.…”

“…1) is introduced with * Electronic address: nishino.masamichi@nims.go.jp microscopic magnetic parameters and the temperature effect can be treated properly in the atomistic modellings. By using the atomistic models, quantitative properties of the Nd magnet have been intensively investigated [16,[22][23][24][25][26][27][28][29][30][31][32][33][34].…”