Electronic structure of charge-ordered Fe3O4 from calculated optical, megneto-optical Kerr effect, and O K-edge x-ray absorption spectra

摘要

The electronic structure of the low-temperature (LT) monoclinic magnetite,Fe3O4, is investigated using the local spin density approximation (LSDA) andthe LSDA+U method. The self-consistent charge ordered LSDA+U solution has apronounced [001] charge density wave character. In addition, a minor [00{1/2}]modulation in the phase of the charge order (CO) also occurs. While theexistence of CO is evidenced by the large difference between the occupancies ofthe minority spin t_{2g} states of ``2+'' and ``3+'' Fe_B cations, the total 3dcharge disproportion is small, in accord with the valence-bond-sum analysis ofstructural data. Weak Fe orbital moments of ~0.07 mB are obtained fromrelativistic calculations for the CO phase which is in good agreement withrecent x-ray magnetic circular dichroism measurements. Optical, magneto-opticalKerr effect, and O K-edge x-ray absorption spectra calculated for the chargeordered LSDA+U solution are compared to corresponding LSDA spectra and toavailable experimental data. Reasonably good agreement between the theoreticaland experimental spectra supports the relevance of the CO solution obtained forthe monoclinic LT phase. The results of calculations of effective exchangecoupling constants between Fe spin magnetic moments are also presented.