Permanent magnets based on rare earth elements (RE), particularly neodymium-iron-boron (Nd-Fe-B) magnets, are essential for high-performance motors and generators for use in electric vehicles and wind turbines. To increase their resistance to demagnetization, heavy rare earth elements (HRE) such as dysprosium (Dy) or terbium (Tb) are partially substituted for neodymium. However, these HREs, although crucial for magnetic properties, are critical materials with supply risks. Hence, the challenge is to reduce their content while maintaining performance, in order to meet the growing demand for high-performance magnets. In this context, the grain boundary diffusion (GBD) process of HREs emerges as the most effective solution. It enables the diffusion of HREs from the surface of sintered magnets toward grain boundaries and then into the magnetic phase grains. This localization of HREs at the grain peripheries improves resistance to demagnetization while preserving high remanence, thereby reducing the required amount of HREs.
The objective of this Ph.D is to provide a comprehensive understanding of the diffusion and localization mechanisms of HREs while limiting parasitic reactions that unnecessarily consume them. The doctoral work will combine a comprehensive experimental approach, including the development of HRE-RE-M (where M is a transition metal) alloys for GBD, the study of diffusion, the characterization of equilibrium phases, and detailed magnetic and thermodynamic analyses, particularly through an in-depth study of phase diagrams. This approach aims to define the optimal compositions and diffusion conditions to achieve the targeted magnetic performances.