Tunable Magnetic Property And Millimeter Wave Absorption Property Of ε-Fe2O3 By Metal Substutution | 87706
Chemical Sciences Journal
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Epsilon-iron oxide (ε-Fe2O3) is one of the polymorphys of Fe2O3, which exists as a stable phase in nanometer-size ~ submicrometer-size region. ε-Fe2O3 receives much attention as a hard mangeitc ferrite, since it exhibits the largest coercive field (Hc > 20 kOe) among magnetic ferrites. In addition, it shows a high frequency millimeter wave absorption at 182 GHz due to zero-field ferromagnetic resonance. Herein, we report the synthesis, magnetic properties, and millimeter wave absorption properties of metal substituted ε-Fe2O3 nanomagnets.[2,3] A series of ε-MxFe2-xO3 (M= Al, Ga, In, and Rh) were prepared by several nanoparticle synthesis methods, such as a combining method between a reverse-micelle and a sol-gel methods. Crystal structure analyses based on X-ray diffraction pattern indicate that subsistution site differs between substitution metal. Among four non-equivalent sites in ε-Fe2O3 (FeA, FeB, FeC, and FeD), In3+ substitutes distorted octahedral FeA and FeB sites, Rh3+ substitutes regular octahedral FeC sites, and Al3+ and Ga3+ substitute tetrahedral FeD sites, which can be understood by the difference of ionic radii. Magnetic properties are also affected by metal substitution. The Hc value is reduced with Al3+, Ga3+, In3+ substitution from 20 kOe to 2 kOe, but Hc value is enlarged by Rh3+ substitution and a large Hc value of 31 kOe was observed. Millimeter wave absorption frequency decreased from 182 GHz (ε-Fe2O3) to 35 GHz by Al3+, Ga3+, In3+ subsutitution, but increased up to 222 GHz by Rh3+ substitution. Such a largely tunable magnetic property and millimeter wave absorption property of ε-Fe2O3 is useful from the viewpoint of material design.
Asuka Namai is currently an Assistant Professor of Department of Chemistry, School of Science at The University of Tokyo. She received her PhD. in Science at the University of Tokyo, Japan, in 2013. Her research focuses on the development and physical and chemical characterization of functionalized nanomaterials, with particular interest in iron oxide-based nanomagnets and magnetism.
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