First‐Principles Calculations and Optical Absorption Spectrum of a Light‐Colored Aluminum‐Substituted ε‐Iron Oxide Magnet

In this paper, we report the electronic structure and optical properties of Al-substituted e-Fe2O3. First-principles calculations of the periodic structure of e-Al0.5Fe1.5O3 reveal that the band gaps (Eg) are 2.6 (480 nm) and 2.5 eV (500 nm) for the up-spin and down-spin transitions, respectively. To investigate the electronic structure, a highly dispersed polymer solution composed of e-Al0.66Fe1.34O3 nanoparticles was prepared. This solution is light orange in color; the absorption coefficients (e) are small with values of 810 and 260 dm3 mol–1 cm–1 at 3.1 (400 nm) and 2.6 eV (480 nm), respectively. The reason why Al-substituted e-Fe2O3 is so light in color can be understood by the disappearance of the energy states in the conduction and valence bands, which originates from the tetrahedral D site. Such a light-colored magnetic material should be useful for colored magnetic toners for color printing.