One-Pot Synthesis and Large-Scale Production Strategies for Preparing Ultrafine Hard Magnetic Sm₂Fe₁₇N₃ Nanoparticles

In this study, we demonstrate a facile strategy for the large-scale preparation of ultrafine magnetic Sm2Fe17N3 particles. During the preparation of magnetic nanoparticles (which includes reduction at a high temperature), a blocking agent (e.g., CaO), which enwraps the intermediate phase and discretizes it from the magnetic phase, is often introduced to control the particle size. Contemporary size-control strategies involve immersing solid Sm–Fe intermediates (e.g., Sm2O3–Fe mixed powder or SmFeO3) in a liquid Ca-based precursor solution followed by a series of chemical reactions. However, a heterogeneous reaction with different phases (e.g., solid–liquid) leads to particulate aggregation, resulting in irregular shapes and broad size distribution of the magnetic particles and deteriorated magnetic performance. In this study, therefore, soluble Ca nitrates were added to Sm– and Fe–nitrate precursor solutions for controlling the size of Sm2Fe17N3 submicron particles. Furthermore, the effect of such an addition on the microstructure and phase formation of the Sm–Fe binary system is elucidated. The resulting solutions were used as starting materials for the nitrate salt-based one-pot preparation process. The final products show a significant enhancement in magnetic performance (1.6 times higher energy product), indicating that the method has great potential for practical and inexpensive large-scale commercial applications.