  Magnetic skyrmions, as a whirling spin texture with axisymmetry, cannot be
propelled by a uniform magnetic field. Therefore, reported skyrmion motions
have been induced using other sorts of stimuli; typically, electric currents in
magnetic metals as well as spin waves, thermal gradient, and field gradient
have manifested their ability to drive skyrmion motion. Here, we demonstrate,
through micromagnetic simulations and analytically, that magnetic skyrmions can
be displaced by a uniform perpendicular magnetic field via a domain-wall (DW)
mediator. For a fixed field strength, the velocity of a skyrmion train evolves
in terms of 1 / (1 + Ns) with Ns denoting the number of skyrmions. Based on
Thiele's model, we reproduce the velocity-Ns relation first identified from
numerical results and reveal that the skyrmion-DW and inter-skyrmion repulsions
offer the direct driving force for skyrmion motion. This study underlines the
role of spin textures' interaction in skyrmion dynamics, and opens an
alternative route for skyrmion manipulation especially relevant to insulating
magnets. Given the correspondence between magnetism and electricity, we
anticipate that the scheme should also work for polar skyrmions in
ferroelectrics.
