Exploring Critical Synthetic Parameters for Nanoscale ε-Fe2O3 and Their Influence on Magnetic Behaviors
- Jamie CleronJamie CleronDepartment of Chemistry, Yale University, New Haven, Connecticut 06520, United StatesMore by Jamie Cleron
- Alexander A. Baker
- Tom NakotteTom NakottePhysical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United StatesMore by Tom Nakotte
- Alyssa TroksaAlyssa TroksaPhysical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California 94550, United StatesMore by Alyssa Troksa
- , and
- Jinkyu Han*
An intermediate polymorph of iron oxide, ε-Fe2O3, has attracted significant attention due to its giant coercive field (Hc) and potential applications in high-frequency millimeter-wave absorption and high-density magnetic recording. However, the fabrication of ε-Fe2O3 with high phase purity is still a challenge due to complicated synthetic procedures and a large variety of reaction parameters. Here, we have identified critical reaction parameters to improve the phase purity of ε-Fe2O3, and the effects of all possible reaction parameters have been tested through systematic studies. A combination of structural and magnetic characterization techniques provides us with an accurate and reliable phase purity analysis of the ε-Fe2O3 phase. Specifically, we observed that (1) the reaction temperature and time and (2) the addition of Ba are critical parameters to improve the phase purity. We identified the optimal conditions that maximize the coercivity and phase purity, giving insight into the effects of each parameter on the γ- to ε- to α-phase-transition pathway. We obtained nearly single-phase ε-Fe2O3 (∼87 wt % with ∼13 wt % α-phase) with a large coercivity of Hc = 20.6 kOe, enabling us to obtain pure ε-Fe2O3 by a simple magnetic separation protocol, and tuned the Hc of the ε-Fe2O3 nanoparticles in the range of 4.0–20.6 kOe by controlling the reaction parameters. Furthermore, the structural properties of the resulting ε-Fe2O3 nanoparticles are confirmed by characterizing their chemical and magnetic properties using X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements.
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