Yasuhara Sou, Hamasaki Yosuke, Katayama Tsukasa, Ao Takahiro, Inaguma Yoshiyuki, Hojo Hajime, Karppinen Maarit, Philip Anish, Yasui Shintaro, Itoh Mitsuru
Laboratory for Materials and Structures, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
Department of Applied Physics, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka 239-8686, Japan.
Inorg Chem. 2020 Apr 6;59(7):4357-4365. doi: 10.1021/acs.inorgchem.9b03302. Epub 2020 Mar 18.
ε-FeO, a metastable phase of iron oxide, is widely known as a room-temperature multiferroic material or as a superhard magnet. Element substitution into ε-FeO 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-FeO in the Fe/Fe coexisting states, Li was electrochemically inserted into ε-FeO to reduce Fe. The discharge and charge of Li into/from ε-FeO 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-FeO 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-FeO is a useful tool for characterizing crystal structure, lithiation limit, and magnetic properties in the coexistence of Fe/Fe.
ε-氧化铁（ε-FeO）是氧化铁的一种亚稳相，作为室温多铁性材料或超硬磁体而广为人知。文献中已报道了元素对ε-FeO的取代；然而，取代离子根据其离子半径和化合价具有很强的位点偏好性。在本研究中，为了表征ε-FeO在Fe/Fe共存状态下的晶体结构和磁性，通过电化学方法将锂插入ε-FeO中以还原铁。锂在ε-FeO中的充放电表明锂的插入是成功的。X射线磁圆二色性结果表明，还原后的铁没有表现出位点偏好性。ε-FeO中锂含量的增加导致饱和磁化强度降低以及矫顽场的不规则变化。我们利用透射电子显微镜图像并考虑锂扩散系数，对随着锂含量增加磁性如何变化进行了全面讨论。结果表明，将锂插入晶体ε-FeO是表征Fe/Fe共存状态下晶体结构、锂化极限和磁性的有用工具。
