Korean Researchers Solve the Thick-Magnet Coercivity Problem with a Sandwich-Structured Grain Boundary Diffusion Process

Why It Matters

Uniform coercivity in thick magnets enables higher torque density and efficiency for EV and industrial motors while cutting heavy‑rare‑earth costs and supply‑chain risk.

Key Takeaways

• Sandwich diffusion embeds Pr alloy between magnet layers for uniform coercivity
• Internal diffusion eliminates performance drop in thick Nd-Fe-B magnets
• High-resistivity layer boundaries reduce eddy currents, improving efficiency
• Uses light rare earth praseodymium, cutting reliance on dysprosium and terbium
• Process merges segmentation, diffusion, and insulating bonding into a single step

Pulse Analysis

The performance ceiling of neodymium‑iron‑boron (Nd‑Fe‑B) magnets has long constrained the design of high‑power electric‑vehicle (EV) traction motors. While grain‑boundary diffusion of heavy rare‑earth elements such as dysprosium can boost high‑temperature coercivity, the process penetrates only a few millimetres from the surface. As manufacturers thicken magnets to increase torque density, the interior remains under‑coerced, leading to magnetic loss and reduced motor efficiency. This scaling dilemma has driven researchers to seek diffusion techniques that can uniformly treat the full cross‑section of thick magnet blocks.

Korea Institute of Materials Science (KIMS) answered that challenge with a sandwich‑structured diffusion method. Multiple Nd‑Fe‑B layers are stacked, and a praseodymium‑based light rare‑earth alloy is applied to both outer faces and each interlayer before the stack is bonded. During heat treatment the alloy diffuses from every interface, establishing consistent coercivity throughout the magnet’s thickness. Simultaneously, the newly formed interlayer boundaries act as high‑resistivity barriers that damp eddy currents generated at high speeds, cutting heat buildup and further preserving magnetic performance. Crucially, the approach replaces costly dysprosium with abundant praseodymium, easing China‑centric supply risks.

The combined benefits position the technology as a potential game‑changer for EV and industrial motor makers. Uniform coercivity enables designers to use thicker magnets without sacrificing efficiency, opening pathways to higher torque densities and lighter motor housings. By collapsing segmentation, diffusion and insulating bonding into a single step, manufacturers can lower production complexity and cost. Moreover, the reduced dependence on heavy rare earths aligns with sustainability goals and mitigates geopolitical exposure. KIMS is now pursuing motor‑integration trials, and if scaled, the process could reshape the magnet supply chain across automotive, wind‑turbine and marine propulsion sectors.