Korean researchers solve the thick-magnet coercivity problem with a sandwich-structured grain boundary diffusion process

Researchers at the Korea Institute of Materials Science (KIMS) have developed an innovative solution to a longstanding challenge in the design of high-power electric vehicle (EV) motors involving Nd-Fe-B magnets. These magnets traditionally suffer from a decline in coercivity—the ability to maintain magnetisation under heat and opposing magnetic fields—towards their core when they are made thicker to handle greater torque. The new technique involves a sandwich-structured grain boundary diffusion process, where a praseodymium-based light rare earth alloy is introduced not only on the magnet’s surface but also between stacked layers within the magnet itself. This ensures uniform coercivity throughout the entire thickness of the magnet, overcoming the degradation issues that have limited motor performance. The process addresses a dual challenge in magnet design. In addition to improving coercivity, the layered structure created during the diffusion process increases electrical resistivity, effectively suppressing eddy currents that generate heat during high-speed motor operation. This heat buildup has previously contributed to performance loss, so the new method enhances both magnetic and thermal stability. By combining segmentation, grain boundary diffusion, and insulating bonding into a single step, the researchers have streamlined what were previously three separate manufacturing operations, potentially simplifying production and reducing costs. A significant advantage of this approach is the use of praseodymium, a light rare earth element, as the diffusion medium instead of the more expensive and geopolitically sensitive heavy rare earths such as dysprosium and terbium. These heavy rare earths are typically sourced almost exclusively from China, so this development could reduce supply chain vulnerabilities and material costs for manufacturers. Although specific coercivity and resistivity values have not been disclosed, the researchers highlight the broad applicability of their technology, which extends beyond EV traction motors to industrial motors, wind turbines, and even electric ship propulsion systems. The study, published in Scripta Materialia, was led by Su-Min Kim and Jung-Goo Lee at KIMS and marks a promising advance in magnet technology for electric motors. The team is currently working on integrating this innovation into practical motor designs, signalling potential near-term impacts on the efficiency and durability of electric motors across various industries. This breakthrough could play a crucial role in enabling more powerful and reliable electric drivetrains as the demand for high-performance EVs and renewable energy solutions continues to grow.