Electronic structure and magneto-optical Kerr effect of Fe3O4 and Mg2+- or Al3+-substituted Fe3O4

The optical and magneto-optical spectra of charge-ordered magnetite (Fe3O4) below the Verwey transition and Mg2+- and Al3+-substituted Fe3O4 are investigated theoretically from first principles, using the fully relativistic Dirac linear muffin-tin orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+U approach for which the charge ordering is found to be a stable solution with an energy gap value of 0.19 eV (the experimental value is 0.14 eV) in contrast to a metallic state given by LSDA. The origin of the Kerr rotation realized in the compounds is examined