Synthesis of Mesoscopic Particles of Multi-Component Rare Earth Permanent Magnet Compounds

Abstract

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 ((BH)_max), 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 (H_c) and remanence (M_r), respectively, remains marginal.