Solution-Phase Metathesis of Li₃N and FeCl₃ to Synthesize Fe₂N/Fe₃N Nanoparticles

Soft magnetic materials play key roles in the flow of energy in electrically driven machines and power conversion electronics, and there is a great need for improvements in their magnetic properties to provide the right combination of high saturation magnetization, low coercivity, and high permeability. Most phases of iron nitride (Fe_xN) are soft magnetic materials with these characteristics, but they exist as numerous phases which are not all stoichiometric compounds. While the production and magnetic properties of the different phases of bulk iron nitride are well known, accessing phase-pure nanoscale iron nitride consistently remains a challenge. Most methods for the synthesis of iron nitride nanoparticles require complicated apparatus to achieve high-temperature nitriding of nanoparticle precursors with gaseous nitrogen sources such as ammonia. The first solution-phase metathesis reaction between FeCl₃ and Li₃N in oleylamine is developed to directly synthesize Fe₂N/Fe₃N nanoparticles, requiring only a fume hood, glove box, standard chemistry laboratory glassware, and equipment. The ≈10–15 nm spheres display nearly soft magnetic behavior with a saturation magnetization ≈50–60 A m² kg⁻¹, coercivities between 40–50 kA m⁻¹, and susceptibility values from 0.0001–0.0006 m³ kg⁻¹, well within the ranges reported with other published Fe_xN nanoparticle synthesis methods.