ε-Fe2O3, a metastable phase of iron oxide, is widely known as a room-temperature
multiferroic material or as a superhard magnet. Element substitution
into ε-Fe2O3 has been reported in the
literature; however, the substituted ions have a strong site preference
depending on their ionic radii and valence. In this study, in order
to characterize the crystal structure and magnetic properties of ε-Fe2O3 in the Fe2+/Fe3+ coexisting
states, Li+ was electrochemically inserted into ε-Fe2O3 to reduce Fe3+. The discharge and
charge of Li+ into/from ε-Fe2O3 revealed that Li+ insertion was successful. X-ray magnetic
circular dichroism results indicated that the reduced Fe did not exhibit
site preference. Increasing the Li+ content in ε-Fe2O3 resulted in decreased saturation magnetization
and irregular variation of the coercive field. We present a comprehensive
discussion of how magnetic properties are modified with increasing
Li+ content using transmission electron microscopy images
and considering the Li+ diffusion coefficient. The results
suggest that inserting Li+ into crystalline ε-Fe2O3 is a useful tool for characterizing crystal
structure, lithiation limit, and magnetic properties in the coexistence
of Fe2+/Fe3+.