Synthesis and Characterization of Size-controlled Sm2Fe17N3 Nanostructure via Solution Combustion method

Abstract

Sm-Fe-N magnets are promising candidate for next-generation permanent magnet against Nd2Fe14B and Sm-Co magnets, which are used in various magnetic applications such as electric vehicles due to its superior magnetic characteristics. This study reports a method for synthesizing Sm-Fe-N nanoparticles through solution combustion, reduction-diffusion, and nitriding processes, and introducing CaO to prevent agglomeration between the resulting particles. Conventional top-down approaches that require a pulverization process lead to deterioration of magnetic properties due to phase inhomogeneity, surface defects and previous chemical methods such as co-precipitation and polymerized-complex have complex process or low production yield. And also, fabricated Sm2Fe17N3 nanoparticles have a wide range of particle size distribution in these process owing to particle sintering and aggregation originated from over-growth of iron particles during heat treatment for reduction. Herein, a process using Solution Combustion method and Reduction-Diffusion was proposed to synthesize Sm2Fe17N3 nanoparticles with well-controlled size. At first, porous oxide precursor was prepared via solution combustion reaction by using of metal nitrate sources and organic fuel. Thereafter, through two reductive annealing processes and consecutive nitriding without exposure to air and rinsing solution, Sm2Fe17N3 nanostructures were synthesized. Synthesis mechanism was investigated by analyzing crystal structures and morphologies of precursors and products in each process, and for synthesis of single phase Sm2Fe17N3 magnet, the process was optimized. CaO which added as a growth inhibitor wraps around Fe core well, completely controlling the over-growth of Fe particles. The Sm2Fe17N3 nanoparticles, which synthesized from precursor solutions having the Ca/Fe molar ratios of 0, 0.5, and 1, had the average diameter of 835, 612 and 473 nm, respectively. The calculated saturation magnetization(Ms) values were 133, 134, and 135 emu/g. The squareness(Mr/Ms) were 0.767, 0.796, and 0.798. Each nanomagnet exhibited high coercivity(Hc) of 13.7, 13.1, and 14.8 kOe, and resulting maximum energy product((BH)max) were increased from 8.68 to near 13 MGOe. Therefore, Sm2Fe17N3 magnets were prepared through solution combustion and reduction-diffusion process, and magnetic performance was improved by controlling size of Sm2Fe17N3 particles in a submicron scale using a Ca-based growth-inhibitor. In this study, a facile method, which can reduce problems that may occurred in conventional processes and synthesize nanoscale oxide precursors and less-aggregated Sm2Fe17N3 nanoparticles, was introduced. It suggests a new strategy to manufacture Sm2Fe17N3 magnets for high-performance nanomagnets with simple process control. Furthermore, it has the potential for use as a bulk magnet by increasing the driving force for sintering through particle control.