Exploring Critical Synthetic Parameters for Nanoscale ?-Fe2O3andTheir Influence on Magnetic Behaviors

An intermediate polymorph of iron oxide,epsilon-Fe2O3, has attracted significant attention due to itsgiant coercivefield (Hc) and potential applications in high-frequency millimeter-wave absorption and high-density magnetic recording. However, the fabrication of epsilon-Fe2O3with high phase purity is still a challenge dueto complicated synthetic procedures and a large variety of reaction parameters. Here, we have identified criticalreaction parameters to improve the phase purity of epsilon-Fe2O3, and the effects of all possible reaction parametershave been tested through systematic studies. A combination of structural and magnetic characterizationtechniques provides us with an accurate and reliable phase purity analysis of the epsilon-Fe2O3phase. Specifically, weobserved that (1) the reaction temperature and time and (2) the addition of Ba are critical parameters toimprove 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 gamma-to epsilon-to alpha-phase-transition pathway. We obtainednearly single-phase epsilon-Fe2O3(similar to 87 wt % with similar to 13 wt %alpha-phase) with a large coercivity ofHc= 20.6 kOe,enabling us to obtain pure epsilon-Fe2O3by a simple magnetic separation protocol, and tuned theHcof the epsilon-Fe2O3nanoparticles in the range of 4.0-20.6 kOe by controlling the reaction parameters. Furthermore, the structuralproperties of the resulting epsilon-Fe2O3nanoparticles are confirmed by characterizing their chemical and magnetic properties using X-rayabsorption spectroscopy and X-ray magnetic circular dichroism measurements.

Automated summary

The critical reaction parameters to improve the phase purity of ε-Fe2O3 were identified and their effects were systematically studied. Under optimal conditions, high-purity ε-Fe2O3 could be obtained and separated using a simple magnetic separation protocol.