Solvent Oxidation-Directed Synthesis of Highly Crystalline Iron Oxide Nanoparticles With Near-Bulk Magnetization

Achieving iron oxide nanoparticles with well-defined morphology and near-bulk saturation magnetization remains challenging. Here, we report a simple Fe(acac)₃-based thermal decomposition strategy that produces highly crystalline Fe₃O₄ nanoparticles with tunable sizes and near-bulk magnetization. We identify solvent oxidation as the critical parameter governing this performance. We reveal that the polar oxygenated species generated during controlled oxidation of the solvent benzyl ether (BE) can coordinate to Fe centers and form new intermediate complexes immediately upon simple mixing. These complexes can alter nucleation-growth kinetics, reducing nucleation density while accelerating particle growth, thereby enabling size control without compromising crystallinity. Consequently, the resulting nanoparticles maintain high crystalline quality and magnetite-rich stoichiometry, accounting for their enhanced magnetic performance. Moreover, the strategy is compatible with conventional facet-tuning methods and extendable to doped ferrite systems. Unlike iron oleate routes, which often yield non-stoichiometric particles with reduced magnetization, or systems requiring complex surfactant engineering, our approach achieves high magnetization through straightforward solvent oxidation control. This work provides a simplified strategy for achieving structurally uniform, magnetically optimized iron oxide nanocrystals.