  A three-dimensional topological insulator manifests gapless surface modes,
described by two-dimensional Dirac equation. We study magnetic textures, such
as domain walls and vortices, in a ferromagnetic thin film deposited on a
three-dimensional topological insulator. It is shown that these textures can be
electrically charged, ascribed to the proximity effect with the Dirac surface
states. We derive a general relation between the electric and the magnetic
charges. As a physical consequence, we discuss domain wall motion driven by an
applied electric field, which promises magnetic devices with high thermal
efficiency.
