Study of the Electronic Structure and Magnetic Properties of ε-Fe2O3by First-Principles Calculation and Molecular Orbital Calculations

Abstract

ε-Fe2O3 is known to exhibit a large coercive field of 20 kOe at room temperature. In this work, we examine the electronic structure and magnetic properties of ε-Fe2O3 using first-principles calculation and discrete variational (DV)-Xα molecular orbital calculation. The first-principles calculation shows that ε-Fe2O3 is a charge-transfer type insulator with a valence band of O2p and a conduction band of Fe3d. The optical transition is an indirect transition from Γ to S point. The density of states (DOS) of the four nonequivalent Fe sites (FeA, FeB, FeC, and FeD) indicates that ε-Fe2O3 has ferrimagnetic ordering due to α spins on FeB and FeC and β spins on FeA and FeD. The charge density map of the occupied Fe3d band displays a strong hybridization between Fe3d and O2p. Molecular orbital calculation for each Fe site also supports the existence of a strong Fe3d–O2p hybridization. Such a strong hybridization induces nonzero orbital angular momentum L on Fe3d through the partial charge transfer from O2p to Fe3d. The appearance of L causes a large magnetic anisotropy through spin–orbit interaction, which induces the large coercive field.