Synthesis of mesoscopic particles of multi-component rare earth permanent magnet compounds

Multielement rare earth (R)-transition metal (T) intermetallics are arguably the next generation of high-performance permanent magnetic materials for future applications in energy-saving and renewable energy technologies. Pseudobinary Sm₂Fe₁₇N₃ and (R,Zr)(Fe,Co,Ti)₁₂ (R = Nd, Sm) compounds have the highest potential to meet current demands for rare-earth-element-lean permanent magnets (PMs) with ultra-large energy product and operating temperatures up to 200°C. However, the synthesis of these materials, especially in the mesoscopic scale for maximizing the maximum energy product ( $$ ), remains a great challenge. Nonequilibrium processes are apparently used to overcome the phase-stabilization challenge in preparing the R-T intermetallics but have limited control of the material's microstructure. More radical bottom-up nanoparticle approaches based on chemical synthesis have also been explored, owing to their potential to achieve the desired composition, structure, size, and shape. While a great achievement has been made for the Sm₂Fe₁₇N₃, progress in the synthesis of (R,Zr)(Fe,Co,Ti)₁₂ magnetic mesoscopic particles (MMPs) and R-T/T exchange-coupled nanocomposites (NCMs) with substantial coercivity ( $$ ) and remanence ( $$ , respectively, remains marginal.