Marie Yoshikiyo
The University of Tokyo, Japan
Title: First-principles calculation of ε-Fe2O3 with a huge coercive field
Biography
Biography: Marie Yoshikiyo
Abstract
Iron oxide materials have contributed to our society due to their chemical stability and economical cost, for example, α-Fe2O3 as pigment and γ-Fe2O3 as magnetic recording material. In 2004, our research group succeeded in synthesizing a pure phase of a different Fe2O3, ε-Fe2O3, which exhibits a huge coercive field of 20 kOe at room temperature.1 Originating from its strong magnetic anisotropy, ε-Fe2O3 also shows electromagnetic wave absorption at a very high frequency of 182 GHz. In this work, we report the theoretical studies on the physical properties of ε-Fe2O3 by first-principles calculation. ε-Fe2O3 has an orthorhombic crystal structure with four nonequivalent Fe sites, A, B, C, and D sites. Based on this crystal structure, we studied the electronic structure by first-principles calculations and molecular orbital calculations to understand the origin of the huge coercive field.2 The density of states showed that ε-Fe2O3 is a charge-transfer type insulator with positive sublattice magnetizations at B and C sites and negative sublattice magnetizations at A and D sites, consistent with our previous study based on molecular field theory.3 The charge density map of the Fe3d band showed a strong hybridization with O2p orbitals. Molecular orbital calculations indicated that this hybridization originates from the distorted coordination geometry of the Fe sites. Due to the hybridization, charge-transfer occurs from O2p to Fe3d generating a non-zero orbital angular momentum, enhancing the magnetic anisotropy of ε-Fe2O3. Furthermore, electric polarization of ε-Fe2O3 was also investigated by first-principles calculation.
