Micromagnetic Investigation on Microstructure Modulation and Magnetic Properties of Nd-Fe-B Permanent Magnets

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• The magnetic properties of rare-earth permanent magnets, such as Neodymium-Iron-Boron (Nd-Fe-B), are intrinsically linked to their microstructural characteristics.
• Understanding the influence of microstructural features like grain boundaries (GBs) and grain orientation is vital for enhancing magnet performance.

Purpose of the Study:

• To systematically investigate the impact of grain boundary characteristics and grain crystallographic orientation on the coercivity (Hc) and remanence (Mr) of Nd-Fe-B-like magnetic materials.
• To elucidate the role of grain boundaries as nucleation sites and pinning centers in magnetic reversal processes.

Main Methods:

• Utilized Hybrid Monte Carlo micromagnetics simulations to model polycrystalline magnetic materials.
• Employed Voronoi tessellation to construct a model with adjustable microstructural parameters, including GB width and grain orientation.
• Analyzed the effects of varying GB width, GB saturation magnetization, and average easy-axis tilt angle on magnetic properties.

Main Results:

• An increase in GB width from 2 nm to 10 nm led to a 32% reduction in Hc and a 16% reduction in Mr.
• Wider GBs were found to facilitate reverse domain nucleation, particularly at triple junctions, and influence domain wall propagation.
• Increasing GB saturation magnetization in thicker GBs weakened exchange coupling, promoting localized nucleation over collective switching.
• A greater average easy-axis tilt angle decreased Hc by reducing the effective anisotropy along the applied field direction.

Conclusions:

• Grain boundary properties and crystallographic texture are critical factors in determining the magnetic performance of Nd-Fe-B permanent magnets.
• The study provides quantitative insights into how microstructural parameters influence coercivity and remanence, offering valuable guidance for experimental optimization.
• Findings underscore the importance of precise control over microstructure for developing high-performance permanent magnets.