Electron theory of magnetoelectric effects in metallic ferromagnetic nanostructures

摘要

The physics of magnetoelectric effects in metallic films is investigated by use of the ab initio spin density functional theory for Fe films and Fe-Au-Fe heterofilms with various thicknesses. Based on the magnetic force theorem for the calculation of the magnetocrystalline anisotropy energy, E_(mca), a method for the definition of layer-resolved contributions to E_(mca) is introduced, and the reliability of this method is discussed in detail. The knowledge of such layer-resolved contributions is important for a theoretical modeling of magnetoelectric effects on an atomic level in systems that are too complicated for an ab initio treatment. Quantities that characterize the anisotropic electron charge density and its magnetoelectric modification are introduced, and these quantities are useful for the interpretation of the magnetoelectric effects on E_(mca) in the spirit of Kind's explanation of E_(mca). Finally, it is shown that for certain average thicknesses of ultrathin Fe films in Fe-Au-Fe it is possible to switch the magnetization between in-plane and out-of-plane directions by rather small electric fields.